On a few different threads recently, questions about acronyms and so on. Granted some of them might not be MN-specific but could be helpful for newbies regardless.
Plus there are some that I just simply don't know and have now been here long enough that it's embarrassing. 
I'll start - in the last couple of weeks I have learned:
GF - Goady Fucker
IPOAT - Insane People on a Thread
Plus I think the following should be on there (or maybe they are, CBA to check TBH)
RTFT
ODFOD
LO
FWR
DH meaning Dog House as well as Darling Husband (misunderstanding that one makes for verrrrrry interesting reading let me tell you)
Any others?