Hardest Achievement?

Garrys Mod
You have to have 1 year of playtime which is nearly 10000 hours in order to get the last achievement!

Either:

Hexagon - finish Super Hexagon

The End - finish Super Meat Boy (NOT the Dark World)

I hate both of them. Currently playing The Binding of Isaac, which is just as frustrating. :(

Complete bad rats. (not done yet...)

Skyrim's marriage achivement.

Super Meat Boy - The Golden Gift

I know many people got it, but there's a big difference: I didn't cheat.

any of Dota 2 achivements - i dont know a guy who completed any of them!

Not buying anything at the year end sale.

Definitely the Mom's Contact's achievement on Binding of Isaac. I can't unlock those things for the life of me.

Back in my day games didn't have achievements I kinda miss that.

universe sandbox:

Startup Too Many

Start Universe Sandbox 10^4 = 10000 times

and:

One Year

Rule over your universe for 12 months

Acheivements from Super Meat Boy

Garry's Mode:Mega Upload (Get 1000 thumbs on a single upload (then go to jail))is pretty hard achievment too :)

any achievement that requires that i dont kill all of everything to death.

Have to agree.. the super meat boy achievements

I think Super Meat Boy ones, even if I didn't take them all (some are too damn hard for me)

In shogun 2 there is a achievement to be 1st on the leaderboards in the world.

I don't have it, but I think probably about the most difficult achievement I know of would be Dungeon of Dredmor's 'Sewer Brew' achievement, though it may vary somewhat in difficulty depending on things like where you live. To get it, you have to drink with someone who works for Gaslamp Games. In real life. Personally, traveling to Canada and hanging around their offices hoping to catch a beer with one of them after work or something just isn't practicable for me, and I imagine most people are similarly hindered.

any bugged achievement from whatever game which won't unlock, no matter how hard you try :|

B.U.T.T.O.N. (Brutally Unfair Tactics Totally OK Now):

"You're So Lucky!
Each round, you have a one in a million chance of getting this achievement. Good luck..."

Hitman: Absolution

Absolution: You completed Hitman: Absolution™ as a professional

Schrodinger's Catch, Portal 2.

Almost any MP achievement.

Those "achieve X views on your youtube video" for Team Fortress 2

Counter-Strike : Global Offensive
The Immovable Object
Kill an enemy who has killed four of your teammates within the current round