AAW - Alive And Well
AISL - After I Stop Laughing
AFK - Away From Keyboard
AYST - After You Stop Talking
CTF - Cheaper Than Free
DLTH - Don't Listen To Him (Her)
DMMKU - Don't Make Me Kick yoU
DYHAP - Do You Have A Point(?)
GAFM - Get Away From Me
IC - I'm Confused
ICTT - I Can't Type Today
IDC - I Don't Care
ITF - In The Face
IHMC - I Hate My Computer
IYPKB - Is Your Period Key Broken(?)
IYSS - If You Say So
FTMTN - For The Millionth Time, No
FTTTN - For The Thousandth Time, No
GAFM - Get Away From Me
GTB - Going To Bed
IASG - I Ate Something Gross
IDC - I Don't Care
IDK - I Don't Know
IDTS - I Don't Think So
IUOK - If yoU Only Knew
IYL - It's Your Loss
IYSS - If You Say So
MBFA - My Butt Fell Asleep
MFG - Mining For Gold
MMGB - My Mind's Gone Blank
NEIYPM - Not Even If You Paid Me
OIYWW - Only If You Want (to) Win
OOTH - Out Of The House
OOYM - Out Of Your Mind
PTMYJ - Please Tell Me You're Joking
QBS - Quit Being Stupid
SIPO - Sorry, I Passed Out
TAS - Take A Shower
TWTF - That Was Too Funny
WTB - Went To Bed
WTN - Way Too n00b, or What The n00b
YCBS - You Can't Be Serious
YDWN - You Don't Want (to) Know

There we go, just a sampling of the many many acronyms floating around the IRC channels. Happy chatting!