HARDEST ACHIEVEMENT YOU EVER GOT.

[Moonlight Butterfly]

I'm not sure if it's hard....but I got the 'deflect a crossbow bolt with your combat knife' achivement the first time I played RE5. My friends noticed it there and went mental at me.
Apperently they had spent ages trying to unsuccessfully complete it on various occasions. I felt kind of bad as I did it completely by accident. lol.

 

[Lilani]

In TF2, I got the Sniper achievement "Enemy at the Gate," which is attained by killing an enemy within the first second of a round. I don't remember getting it, and I'm not totally sure how I got it. The only thing I can think of is sometimes when I play on the medieval map, if I'm on the offensive side I'll stand at the gate and fire arrows over the top of it until the round starts. I'm guessing one of the arrows made contact just as the round started. Otherwise, I have no idea.

 

[Bucht]

Completing some of the levels in CoD 2 on veteran (still need to do the last two), you just need dumb luck to avoid all those bullets flying at you and you also need a lot of patience cause you'll be doing them again and again for hours until you can complete one.

 

[Iwata]

I don't go trophy hunting, but I got a few i'm proud of. Namely, any and every trophy on Demon's Souls. Seriously, you get trophies for nothing these days, but Demon's Souls holds them back until you earn them.

 

[Soxafloppin]

Either Platting AC: Brotherhood, or doing all the Trials for the Plat In Castlevania: Lords of Shadow.

Also Beating the new MK on the hardest difficulty without losing a round (FUCK YOU SHAO KAHN), but after a few attempts i did it.

 

[teqrevisited]

One Light in the Darkness. (WoW)

It took about a week of nightly raiding and it was utter madness. So many people were booted for consistently failing - and not just one or two clouds, someone "accidentally" managed to spawn 8 additional guardians in the same damn fight and was kicked on the spot. For anyone who doesn't know, that is really bad.

But when we did get him it felt great. I don't play anymore but those were some bloody great nights spent with that guild.

 

[Scizophrenic Llama]

Most recently, probably A Monument to All of Your Sins.

What I consider the hardest achievement for me was Rock Band 2's Iron Bladder achievement whilst on drums. I hadn't been playing on expert too long and I was the only one of my friends who could really handle it. So I really only had an option of switching with another person really on in the setlist, which I never did. So I say there for the six and a half hours or so and got my damn achievement. It wasn't so much holding my bladder as it was sheer endurance from the second half or so of the setlist.

Looking back now I could probably do the setlist a few times over with no issue.