I'm sure there have been times when you've joined a game, went to the char select screen, saw your opponent pick, and cursed at the damn game.
 
For me, I think it would have to be Guile. I don't know, something about that guy makes me play more cautiously than usual. A good Guile can play so many mind games with the sonic booms, and most are SO damn patient! I mean, in most cases they just sit at their corner and wait for me to attack! UGHH.
 
I've learned most of their patterns though, and their flash-kicks are pretty shit as air defense, but still....I don't like 'em :P.
 
Anyone have a worst match-up? (Sagat doesn't count btw, too easy of an answer :P)

Zangief as an Abel player. I'm prepared to call it the game's only broken matchup.

Yes, I hate fighting a good guile.

I hate fighting a good M. Bison. Makes me want to cry.

A good Abel always seems to give me problems.

Vega. Fighting Vega usually ends up in me flailing around trying to AA wall moves. God I hate that asshole.

" Vega. Fighting Vega usually ends up in me flailing around trying to AA wall moves. God I hate that asshole. "

" I hate fighting a good M. Bison. Makes me want to cry. "

Me vs. anyone = bad match up for me

" Me vs. anyone = bad match up for me "

 Blanka and E. honda are bad matchups for me. they make me fight very cautiously. 

Any good charge character really, since I can't play any charge characters except E. Honda.

Blanka.. buddy of mine has an insane Blanka. Beating his Blanka is a very joyous event.

Blanka that fucker has been a pain in my ass since street fighter II. I hate that green bastard.

Balrog. The only people using him...well.....they bring some serious skill.

Blanka and Zangief gives me trouble no matter who I'm using.

Heh, seems like 90% of the responses are charge characters....I guess that makes sense. I'm ok with almost all of them, I know Blanka's tactics, Honda isn't too tough, Chun-li is predictable, Vega has a lot of disadvantages, and I know how to play with Balrog (Boxer) and M. Bison (Dictator). 
 
That's just imo, though.

people who play as blanka are assholes

I can narrow it down to five maybe:
 
Balrog - Godmode.
Rufus - Constant rushdown frightens me.
Ryu - He's like a fortress.
Blanka - Fucking magician. 
Honda - SO MUCH DAMAGE.
 
Even Akuma's worst match-ups are only 5-5 though, so I guess I shouldn't be complaining.

I would say  goken. I havent unlocked him so i don't know how he works but all the people that I have played who choose him are beyond good

A good C.Viper, she gets on my nerves.

I'd say my worst match-up would be Blanka. This seems to be the general consensus for most Cammy players on SRK, as I found out when I went there to see what the hell I was doing wrong against him. Lo-and-behold, everyone else was talking about Blanka, too.

Guile is my worst matchup according to stats.  I just dont play as well against guile as I do against others, its a mental block.  My record vs 'rogs is much better.  Also a particular type of Ryu turtle always gives me fits,  Turtle/counter and if they know how to really FADC into the ultra (Red fireballs cancelled etc) I just want to set the controller down, you do one unsafe move and eat a 50-60% combo.  I play alot of rushdown, and you just have to really know how to break those turtles with mixups.  Of the charge characters Blanka is easiest for me, all of his rolls are unsafe against cammy except jab, and her B&B combos beat electricity, and i don't play too many really good ones. 

Mirabella Bison as Mirabella Bison

"also seth is a dick... a good seth that is...and if youre choosing seth chances are youre pretty good with him "

As an E. Honda player I find my worst match ( besides Sagat :P) would be a Ryu. Not so much Ryu's who zone me out with Hadokens and Shoryukens, while they still get me sometimes I just have to be careful and watch what I'm doing. I'll eventually get him and finish him with Honda's ridiculous damage. I have more trouble with them jumping HK happy cross up ones. I seemingly can’t get my buttstomp out in time, hell even when it does I seem to not be able to beat it.

The worst part about this is that I face sooo many Ryu players… You’d think I’d learn how to deal with this lol. Oh well my scrubby Honda is still scrubby :P

In no particular order: 

Chun li-

Blanka-

Zangief-

Dhalsim / Seth-

The characters that beat me the most as a Ryu player would Ken, Blanka, Chun-Li and smart Goukens or Guiles.

E. Honda always fucks up my M. Bison.

Guile, it's embarrassing. That guy and cammy at times are just... big jerks when played properly. I hate having to go to them. A really good Ryu/Ken get me at times but they have to know their shit. Never have a real issue with Sagat :/ ah yeah a good Blanka makes me sad too for the most part.

Playing Bison, Guile players are always so ridiculous.  Blanka is a huge pain in the ass too.

 Chun-Li usually always beats me....well tbh i lose to everyone but i have the hardest time against chun li
 
the 360 dpad as well is the worst matchup....im slowly losing the will to live using it

I'd like to officially add Zangief to the list of tough match-ups. A lot of people think he's free for Akuma, but they just don't know.

A really good Rose always seems to work me pretty good. Mostly because you never really run into a good Rose

Good players.

No mention of Ken despite people all over the board complaining about him. Surprising

" No mention of Ken despite people all over the board complaining about him. Surprising "

" I hate fighting a good M. Bison. Makes me want to cry. "

" @Jolly_Lolly: I'm over it, at this point I just throw out my gt and see what happens. I am just as guilty defending Ken as are the people bashing him....it is growing old.   And yeah, lets play when you get sorted. From what I hear, you are a Sagat player? "

My worst match up? Everyone on my friend's list.

Nina Williams

" @Jolly_Lolly:   When will you be able to play again? "

As an Akuma player, M.Bison can sometimes be a complete PITA.

I mostly play as Zangief, so without any projectile attack, a good Blanka usually tears me to fucking shreds.