Well my big Online/RL faux pas came about when I was talking with my wife about someone who was not high on my respected list. Finally I blurted out "I can't help it, he's a walking AFK." Took me a bit to explain what that meant.

Wite Hachie here are some more used commonly, some specifically for gaming

AFK = Away From Keyboard or A Free Kill
Walking AFK = Someone who is so bad that they are worthless to their team
brb = Be Right Back or Bath Room Break
l8r = Later
ty = Thank you
np = No Problem
yw = You're Welcome
STFU = Shut The F Up which is what I will do now.