O:
OAUS = On An Unrelated Subject
OBTW = Oh, By The Way
OIC = Oh, I See
OICU = Oh, I See You
OMDB = Over My Dead Body
OMG = Oh My God/Oh My Gosh
OMIK = Open Mouth, Insert Keyboard
ONNA = Oh No, Not Again
OOC = Out Of Character
OOTB = Out Of The Box/Out Of The Blue
OT = Off Topic
OTOH = On The Other Hand
OWTTE = Or Words To That Effect
OZ = stands for "Australia"
P:
PEBCAK = Problem Exists Between Chai[收起]