I sailed really far away from my home only to have a Creeper jump into the water and explode my boat.  I was so close to dying and had a bunch of gear.  It took me another thirty min or so just to get home safe. 
 
So terrifying.

I lost 3 diamond picks, a diamond sword, and a bunch of other stuff dying to something I couldn't see in a cave.  I poked my head through a hole in a ceiling of a cave that had water running through it, and I died instantly.  I made it back to where I died, and for some reason 90% of my stuff wasn't there.

God, this game sounds amazing but I can't bring myself to play it o_o

Fucking spiders... I hate spiders... doesn't matter what happened, I think it should just be repeated that I hate spiders in this game. I did lose a lot of stuff because of said spider though, good guess.

Got killed by Lava... twice.. Fuck lava

Creeper exploded by a lower portion of my fort, little did I know that there was lava about 4 blocks below my basement...

I have lost a full set of gear with diamond picks twice, once from a mob of goo and zombies, and another to a skeleton, one time i returned my stuff was gone, the other time i couldnt find where my old hide out was. Minecraft sure knows how to make you feel like failure. 

hmm.. nothing terrible ever happened to me 

My pet pig lured a giant spider into my castle, the spider then ate my face.

" God, this game sounds amazing but I can't bring myself to play it o_o "

I have a small sized tower which I often use to look around. Just about an hour ago I got too close to the edge of the tower and a skeleton immediately shot me off it, then I feel into my own trench that I built around my house (which I use as a mob collector to gather items) and I landed right next to a creeper who blew me up along with a huge chunk of my house.
 
And that just felt downright BRUTAL, such a great combo of attacks that managed to take me down in less than a second.

Was returning the to the surface after I fell into a new cave system, digging upwards and replacing blocks below me intending to go back down.... I dug myself straight into the bottom of the sea and drowned.

I dug a really, really long tunnel from my base. I emerged in a big, twisting cave system, followed that for awhile, and was killed. I respawned, went into my base and retrieved a couple of picks and a sword. I went back through the really, really long tunnel, into the cave system, and tried to find my stuff. Unfortunately, I fell in a hole and was carried far through another big cave by some water. I emerged in a big valley, saw some pigs and went after them to restore my health. I got lost and couldn't find the cave I'd come out of. I dug a small shelter, sealed it off, and saved my game. That's the last thing I did. My current plan is to find myself the items I need to make a compass and get myself back home.

ventured too far out and forgot which way to go to get home... and death ensued.  
Thats the best i got 

I've been exploring the same cavern for a few days now.  I've died and lost a bunch of equipment a few times.  The 2 times that scared the shit out of me the most were: 
 
A.  I was deep into this thing and had just uncovered a new hole in the ground.  I was foolishly still exploring with HALF of 1 heart of health when I saw the beady eyes of a spider...now spiders are fucking fast.  I turned and ran and for about 30 seconds i didn't look back...i was terrified but managed to navigate the geometry just well enough to jump over a gap that the spider got caught up on...I literally almost shit myself. 
 
B.  Digging around some gravel and poking through walls in the same cavern.  I break through to a new hole, when all of a sudden the roof caves in and water comes splashing through.  I'd never seen it do that before.  I was under the impression that those kind of physics weren't in the game yet but maybe gravel is different.

You guys are having some pretty epic sounding adventures. Jeez.

Everything bad that has happened to me has been because of creepers. I fucking hate creepers. 
 
The other day I found a mine and was going to steal the idea that I saw 'X' do by building a glass roof on top of it. I make my way all the way up there, a skeleton kills me. All good, unfortunately I had all my glass on me but I will just got pick it up. Return to the spot after taking then minutes I get blown up from a creeper that I didn't see and when I finally get back again, the only thing I couldn't find was the glass. I gave up on the project for now. 
 
So I'm building the first portion of this. (Im so proud, but I plan to adjust some of it still) 
 
  http://img.photobucket.com/albums/v118/Sanious/Minecraft/minecraft10.jpg
 
A creeper sneaks up behind me on the tower to the left, blows up, thankfully doesn't kill me, but blows up a portion of my tower and part of the hill. So now I have to fix the hill as well as my tower to even it out.  So I collect all my blocks again, rebuild it and I'm returning home to get health, boom another creeper and this one does kill me. Sooo I go back and thankfully this wasn't near my construction so nothing blows up, yet another creeper comes out of no where, but this time I saw him and lead him away from my castle before I fought him.  
 
I hate creepers! 

Had my save get corrupted during a power outage :'(
 
 
But I managed to restore the save :D (Backups are useful!)
 
But thats not a very good worst thing story...
Worst thing ever is when I was digging in my mine (about 50 paces or so from my awesome sky city) when I hit a bunch of underground springs in a cavern. I had on me at the time a bunch of diamond gear and a lot of cobblestone, redstone etc I was saving up for construction projects... I didn't think much of the water at the time but I also found a cavern which this water flowed into... explored the cavern found lava... somehow at some point managed to find myself in the water which pushed me straight into the lava and I couldn't get out thanks to the water pushing me. Why the lava wasn't hardened into obsidian I'll never know.
Maybe it just decided to make me sad. 
 
But yet, I still hate creepers more!

Nothing too terribly exciting happened to me, but I do have a pretty cool story.  So that I don't bore you, I'll just give you the Cliff's Notes version. 
 
I got bored with the area immediately surrounding my fortress and just decided to hoof it as far out as I could to see what was going on. It started to get dark so I found a cave to hang out in for a bit. Exploring the cave, I found two of those mob spawner doodads in pretty close proximity. Through sheer stupidity (not knowing what to do as I had never seen a mob spawner before) I got blown the fuck up and died. I was kinda bummed because there could have been some rad crap in the chests (of which there were three) and I had absolutely no idea how to get back to that cave.
 
Anyway, I was bummed and I had been playing for about four hours so I decided to take a break. About five hours later I say, "Fuck it" and I reload my game. I have been taken to my spawn point and it is dark, but having said "fuck it" I decide to make some more axes and torches and just start running in what I believe is the general direction that I initially ran to get to the previously mentioned cave. I saw a rock formation in the ice that looked familiar and ran past it. Then I saw a mountain that looked familiar and ran past it. I saw another mountain that looked familiar and ran past it while veering to the left. 
 
About four minutes after taking off and running full-bore, I come to a landmass and start looking around. I see several caves. Sure enough, the very first one I stepped into was the one with all the chests and crap. It is at this point that I realize that I had forgotten to bring a compass. Rather than die and have to find the place again, I just built a huge-ass spire to mark the location of the cave and then I placed a huge line of blocks on the ice leading the way to spire so that I would be able to find it again. 
 
This may not sound that exciting to a lot of you, but finding this cave again was kinda like finding a needle in a haystack. I'm still kinda shocked that I was able to do it. It turned out that there was a gigantic network of tunnels under this landmass and I eventually ended up setting up a second base over there as it took about three days (in real-life, not in-game) to explore the whole thing.
 
Also, I think that skeletons are my least favorite enemy. The creepers are bad, but if you see them in time, you can take them out pretty easily. I haven't had too many problems with spiders either. The skeletons are the ones that can really wreck your shit. Actually, they can all wreck your shit, but the skeletons have the ranged attacks and I've been knocked off of ledges and into creepers a few times. Be careful out there duders!

Also, I think that skeletons are my least favorite enemy. The creepers are bad, but if you see them in time, you can take them out pretty easily. I haven't had too many problems with spiders either. The skeletons are the ones that can really wreck your shit. Actually, they can all wreck your shit, but the skeletons have the ranged attacks and I've been knocked off of ledges and into creepers a few times. Be careful out there duders! "  

The part where I played Minecraft.

I had gotten attacked in one of the caverns I was exploring. Went back home and realized I didn't have any food to heal myself. So I went out searching for a pig. It was close to night but I figured I would be fine. I searched for a good 5 minutes and ended up getting taken down to half a heart by a skeleton. I ran home trying my damnedest to avoid monsters. When I got back, what did I find jumping around in my house? A fucking pig. Sonofa bitch.

Fell into a cave system while mining, cave, as it turned out, was GIGANTIC and the fall drained half of my health. I then heard a spider and a skeleton, which both decided that my scrawny ass was their next lunch. I fought as best I could, but then fell again through a hole I didn't see and, well, lava.

" I had gotten attacked in one of the caverns I was exploring. Went back home and realized I didn't have any food to heal myself. So I went out searching for a pig. It was close to night but I figured I would be fine. I searched for a good 5 minutes and ended up getting taken down to half a heart by a skeleton. I ran home trying my damnedest to avoid monsters. When I got back, what did I find jumping around in my house? A fucking pig. Sonofa bitch. "