cidefi, here babes:
IRL - in real life
NSFW - not suitable for work
YMMV - your mileage may vary
LOL - (if you don't know what this one means I need you to get off the internet) lol!!!  
IIRC - if I recall correctly
GTFOHWTBS - get the ____ outta here with that bull _____
OTOH - on the other hand
FWIW - for what it's worth
GBCK - this one's Knot specific, it means goodbye cruel knot.  you know this from personal experience, but apparently some of the other boards delight in their ability to see if they can hmm, I think the word I want is *encourage* a poster (usually a newbie but not nec.) to say or demonstrate these words before storming off in a kind of cyber-huff:  {{use your Scarlett O' Hara voice}}  As God is my witness I'll never post on these boards again, you're all horrible people, (there might even be some additional points involved if the poster makes reference to how horrible her attackers are and states some astonishment as to how their husbands can stand them, but i'm almost positive that the extra spin bonus round must contain the words goodbye cruel knot, verbatim).  Don't let the description put you off, my 13 year old daughter insists that this is not only mature, but also hilarious.   
IKR - I know, right?
IDK - I don't know
KWIM - know what I mean?
IOW - in other words
NWR - not wedding related. 
HTH - hope that helps/helped
there's a ton more.  s'all I can remember off the top.  was gonna put it in order but fugg it, ya'll know the alphabet.  anybody, feel free to add on.   Gotta go, I'm gonna go pop some tags, I only got twenny dollas in my pocket.   
TPTB - the powers that be
OT - off topic
SN - side note
CN - cliff note