NOYB = None Of Your Business
NP = No Problem
NQOCD = Not Quite Our Class Dear
NRG = Energy
NRN = No Reply Necessary
NYCFS = New York City Finger Saluet
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
P:
PEBCAK = Problem Exists Between Chair And Keyboard