BRB - be right back
BIO - going for bio break (washroom break)
AFK - away from keyboard (I am gone for a few minutes)
BTW - by the way
KK - OK (commonly used by online gamers to acknowledge that a message has been received)
TTYL - talk to you later
BFN - bye for now
TTFN - ta-ta for now
CYA - see ya (or it could also be: cover your a*s)
CUL8R - see you later
IBTL - in before the lock (for when you post a message prior to the administrator locking the heated discussion thread)
IMHO - in my humble opinion
IMNSHO - in my not so humble opinion
FMV - fair market value (for selling items online)
LOL - laughing out loud
MT - mistell (commonly used by online gamers to say that they made a mistake and mistyped their last message)
NWT - new with tags (for selling items online)
NWOT - new without tags (for selling items online)
OOAK - one of a kind (for selling items online)
PMSL - P*ssing myself laughing (a common UK expression)
QFT - quoted for truth (a compliment to another person on the forum)
ROFL - rolling on floor laughing
ROFLMAO - rolling on floor laughing my a*s off
RTM - read the manual
RTFM - read the f***ing manual (to show frustration at someone's ignorance of basic knowledge)
GG - good game
THX - thanks
TX - thanks
TY - thank you
NP - no problem/you're welcome
PLZ - please
W/E - whatever
ASL - age / sex / location?
RL - real life
IRL - in real life
TTYL - Talk To You Later
ITSFWI - If The Shoe Fits, Wear It!
WIBAMU - Well, I'll be a Monkey's Uncle!
POSSLQ - Person of Opposite Sex, Sharing Living Quarters
