My funniest moment would probably have to be the scene when EDI cracks the joke "I love the sight of humans on their knees." Joker's face was priceless!

Its a quick moment but Grunt and Shepherd throw each other a quick glance before diving to either side to start a fire fight. It was like something out of an Abbot and Costello routine and I admit I giggled.

The funniest moment for me was Mordins singing, which just blew my mind :) Model scientist Salarian indeed.
The second moment for me was the reunion with Conrad Verner. The way he totally described my lifestyle (Living on the edge, looking for Credits in crates) was just awesome.

my favourite part was when evil "titi shepard" started dancing like a retard with a girl in a club only to be brutally shot down.
 
But almost all parts of this game are hilarious when your shepard looks like a cross eyed monkey. Especially when he has just been introduced as the saviour of the galaxy and had many resources put into reconstructing him. Not to mention he is an utter asshole uninterested in anyone.

mine would be listening to the bachelor party found in Illium where a Human, Salarian, and a Turian debate about sexual attraction to Asari. :p

Joker doing the robot dance at the beginning of Legion's side quest. That was pretty good. 
Shepard kicking that Varren during the side quest where you need to save the quarian. They probably did not intended that as a joke but it was illarious.

" Joker doing the robot dance at the beginning of Legion's side quest. That was pretty good. Shepard kicking that Varren during the side quest where you need to save the quarian. They probably did not intended that as a joke but it was illarious. "

Shepard.
 
I should go.
 
Shepard.

Two worth mentioning: 
 
Garrus and Tali talking about elevators while walking around the citadel. "I have a shotgun now."
 The quarian and turian on...Illium, I believe? Could be the Citadel as well. Anyway, the one where the turian clearly is into the oblivious quarian, who's having romantic frustrations.

Most of the stuff between EDI and Joker was great.
 
And while the moments surrounding the moment were anything but hilarious, EDIs whole "I enjoy seeing humans on their knees" got me.

The first time I took Jack into combat, I went around a corner and saw some bad guys and Jack said, "Hello dead people."

"I had reach, but she had flexibility"

I was completing Grunt's loyalty missions and right when you're talking to the head honcho to start the contest rites thingy, his henchmen was shit-talking about him being tank-born. My female Shepard just looks at him and just dives her face forward and headbutts him... *THWACK!* He's like, "did you just... really? You just did what I think you did."

definitely has to be punching the reporter in the face......for the second time :D

So far, I would say Shepard head-butting the Krogan during Grunt's loyalty mission, or a simple little throwaway line I just heard from a Salarian shop owner on the Citadel: "It's stunning how many people think light moves faster though expensive fiber optic cables than it does through cheap ones."   Made me laugh, because 1: it's completely true, and 2: it applies to cables today, along with a lot of other things... xD
 
So many amazing little dialogue lines, facial reactions... for such a dramatic game, it has some damn funny moments.  =D

lol after pursuing a relationship with jack i noticed my picture of ashely williams in my cabin was face down on my desk. ps more ash in ME 3 pls my favorite anti alien bud

Mordin's singing was probably one of the greatest moment in a video game ever.  But the stuff that really made me laugh was the stuff between Joker and EDI.

Bringing Legion onto the Quarian Ship and them not caring.    

So I romanced with Jack. (Who can turn down her eyes, lips and voice? Who cares that she's got tattoos everywhere or is bald!) This actually happened after I finished the game and after Shepard and Jack got together however:
 
I went in to talk to Mordin and he was like "actually yes I do want to talk to you." I don't remember the whole conversation but Mordin essentially went off and talked about how he knew Jack and Shepard were sexually active and how he had medical things to protect Shepard during relations because biotics are more "uncontrolled" during sexual activities. There was a lot more to it, and obviously I did a horrible time explaining it, but the conversation was just absolutely hilarious. It was fabulous. Icing on the cake for what is a fabulous game.

Bringing Legion to the recruit Tali mish. Got to Kel'raeger(sp?) and he says "uh theres a Geth right behind you" then later on when you get Tali she freaks out because of Legion. Legion just says "Do not worry we do not wish to kill the creators at this time" or something to that effect

" There was a moment in the citadel where an Alliance sergeant was "educating" his charges on the physics of vacuum naval gunnery combat that went something to the effect of:  "Newton's Third Law states that an object will remain in motion unless acted upon by an outside force! So if a shell get's fired, it will not stop until it has hit a ship, or the planet behind that ship, or in 10000 years land on someone else's he's head! So whatever way you look at it, you are ruining somebody's day with this weapon! So no! You do not have the luxury of 'eye-balling' it!" "

Mordin's song.

I haven't finished yet but two stand out to me so far. 
 
I was trying to get into the quarantined area at Omega and finally just snapped: 
 
"Do we look like looters?" 
 
The guard stares at Shephard and my group for a second and just says: 
 
"Um.....   no."  and sheepishly opened the door. 
 
The other was accusing one of the shop employees in citadel of being classist, yelling it in the streets and eventually getting her employee discout at the store to shut me up.  Shephard says something like "Thanks, but you really hurt my feelings"

" Shepard.  I should go.  Shepard. "

NO! The funniest moment is when shephard is in lower afterlife and he fucking dances. Noone can dance better than shepherd!

Agreed with all above priceless moments all : ) 
But personally (Yes im aware it was mentioned before) 
Head butting a Krogan. Was bloody awesome : )

"

Bringing Legion onto the Quarian Ship and them not caring.    

"

the funniest thing I ever witnessed was an advertisment in the Citadel, an Elcor production of Hamlet.
 
Also, a Turian trying to get into the Citadel: "How dare you! This is a religious Heirloom!" and getting the response "Sir, that's a 25 inch serrated blade". 

When you meet Wrex, he hits another annoying krogan in his stupid face, telling him to speak when he is spoken too. Shepard (both male and female) just walks past that krogan with such an assholish smile. That blasted me.

I liked the " My name is commander Shepard and this is my favorite store on the citadel " especially when I had done it with every store.

Oh god, for such a serious game, almost every single person I've talked to has made me laugh.
 
A bit under 15 hours playtime and I just now got around to going to Tuchanka (Krogan homeworld). I laughed pretty loudly when I talked to the Krogan mechanic working on that giant truck.
 
"I've never seen a Krogan mechanic before."
"What, you think we just kidnap Quarians and make them do the 'hard work'? Not anymore we don't." The way he says the last part is awesome.
 
Oh, and almost any Joker-EDI conversation.
 
Oh man, I just totally pet a Varren, then told it to 'Stay'. That's great. Oh yeah, and earlier I totally punched a monkey-looking thing while in the Krogan medical area. Pyjaks they're called. And I murdered like, 40 of them with emplaced cannons.
 
I love all the little things, from EDI telling you that you're in the wrong bathroom to Varren "dogfights", to the subtle nods to random quests that I did in ME1 (like that girl whos husband was killed by some kind of genetic disease, and she was scared for her kid). I also love how there are more random conversations now (at least it seems like it).
 
I have to point out, Tuchanka is completely different from what I thought it would be.
 
Edit: @Toxic: Oh god, I loved that part. Shepards the slickest dude ever to get a deal with every store in the wards like that.
 
Edit 2: Bahaha, I'm in the hospital, and I come across the Krogan scout you were asked to look out for. He kept saying he was too weak and pathetic to go back to the clan, but I managed to convince him.
 
Shepard: It would take a real badass to get all the way back to camp while sick.
Krogan: I...can do it.
Shepard: I said badass, not a little guy whining like a Quarian with a stomache ache.
Tali: Hey, I'm standing right here!
*Krogan says something then runs off*
Tali: I can't believe that actually worked.
 
I love this game.

The Conrad Verner stuff is all pretty great, I laughed out loud. Something like "I just run up and talk to everyone, people just stand around waiting for you to say something! I also like to look inside crates for credits." Awesome. ME2 is surprisingly hilarous from moment to moment, game has a great sense of humor.

I thought the Gamestop burn on the citadel was pretty funny. Even in the far flung future they'll still be asking you to trade in shit towards other shit.

Moridin singing was funny but my favorite is on Illium at the bar.  There's a Turian, a human and a salarian getting a table dance from an asari for the Salarian's bachelor party and (not exact quotes): 
 
H: You see that dent there? 
S: The thing on her abdomen? 
H: Yeah, that's called a belly button.  Only humans and asari have them and later on you're gonna be takin shots out of it! 
T: That doesn't sound very sanitary 
H: Not the point, man.  Not the point.

when you have to break up the fight between Jack and Miranda. On the way there Joker says:
Take pictures. 
 
Brilliant.

During Mordins loyalty mission you find a sick Krogan, get this dialogue with Tali in your party.
 
Shepard: "It would take a real badass to make it back to that camp injured"
Krogan: "I can do it"
Shepard: "You? I said a badass, not a Krogran whining like a Quarian with a stomach ache"
Tali: "I'm standing right here!"

The Elcore   Spectre - "  Enkindle this!" made me laugh so hard! 
 
Joker talking to EDI - "if you start singing Daisy Daisy..." 
 
 Garrus romance conversation - "You know me, I always like to savor the last shot before popping the heat sink. ... Wait. That metaphor just went somewhere horrible."     
 
When you Scan Uranus EDI says "Really commander?.... Fine, Probing Uranus." 
 
 Joker -  "Well, Garrus finally pulled that stick out of his ass. Now he's beating people to death with it. I actually miss the old Garrus."     
 
 "I'm Commander Shepard and this is my favorite store on the Citadel."  *Runs to next store* "I'm Commander Shepard and this is my favorite store on the Citadel."  *Runs to the next store* "I'm Commander Shepard and this is my favorite store on the Citadel."  
 
Tali and Garrus Citadel conversation
   
Garrus: Do you ever miss those conversations we used to have on the elevators on here?

Tali: No.

Garrus: It was a chance to grow closer, you'd tell us about life on the flotilla.

Tali: This conversation is over.

Garrus: Comeon, tell us about your immune system!

Tali: I have a shotgun.

Garrus: Ummmm, right, I'll shut up now.

I laughed out loud when on the Citadel at several of the custom tailored advertisements. 
 
Can't beat Mordin's singing though. Or his speech about mood music being required after you've gone mattress mambo with an alien species. Best Character in the game 

"Don't embarrass me in front of the stripper!"

I just found it amusing that you can put a mining probe on Uranus. hehe. 

" I just found it amusing that you can put a mining probe on Uranus. hehe.  "

^ Local Cluster

Definitely when talking to Mordin about having romance with Garrus.
 
Mordin: "Turians based on dextro-amino acids. Ingestion could cause anaphylactic shock. Don't *cough* ingest."

My Female Renegade Shepard Headbutting Michael Dorn who voices a Krogan.
 
Read that line over and over again, and realize how fucking amazing that sounds.

" Mordin's song. "