I have a couple.
Bioshock - Brass Balls *Complete the game on Hard difficulty without using a Vita-Chamber* Most worth it
Portal - A Feeling Like Floating *Dissolve a Turret* It made me laugh
Borderlands - You're On A Boat! *I bet you never thought you'd be here.* Never listened to the song but I know it.
Bioshock 2 - 9-Irony *Paid your respects to the founder of Rapture.* I just wish the recording would keep saying "A MAN CHOOSES!"
Mass Effect 2 - Missing in Action *Save your crew from an overwhelming attack* When watching Shepard died I made a joke to my friend who was watching and I said "Achievement unlocked You ate shit." then that achievement popped up and we burst into laughter.
And I don't think this has been mentioned yet this is in fact an Xbox thread. Achievements.
I have achieved all these achievements and since I need friends you can check Coratto on Xbox Live
