"Shadowrun Fever"
It's an STD 'achievement' in Shadowrun that you get for teabagging (squatting up and down on someone's face) someone who already has the fever.
Initially it was only the developers who had the fever, but they were teabagged and then those people were teabagged until it spread all across Shadowrun. Nowadays, you can teabag just about anyone and get the Fever. 25 Gamerscore!
Also in Gears of War, one that I liked the best that you missed:
There's an achievement called Series of Tubes I believe, host 50 multiplayer matches. I think it's based on the idiot who called the Internet a series of tubes:
http://en.wikipedia.org/wiki/Series_of_tubes