The only remarkable achievements I've pulled off have been beating chaotic games at extreme levels of intoxication. A buddy and I marathoned Left 4 Dead 2 and beat the entire game while finishing off damn near a refrigerator of leftover half bottles and assorted beers from a party. Myself and this individual alongside 3 other friends also managed to beat the original Little Big Planet while simultaneously finishing a pony keg and about 3 bottles of liquor. The odd man was the dude that either needed to take a piss or make a new drink.
We are only absolutely certain that we beat these games because they had not been played on my friends systems prior to these nights, and we found completed save files the next morning. No one really remembers actually finishing them.