Here are a few I have picked up over the years-- Some might apply to this forum, some might not.
PKB Pot calling the Kettle Black
IKYABWAI an "iky" or "pee-wee" = I know you are, but what am I? Used to point out someone using this juvenile tactic. They have pulled a "pee-wee"
PPOSTFU Post Proof Or Shut the F! Up. ( I can see this one being used..respectfully, of course.)
YHBT You Have Been Trolled
HAND Have A Nice Day
HTH Hope That Helps
IIRC If I Recall Correctly
TTFN Ta Ta for Now -- Signing off.
TTT To The Top-- Like this thread was brought back "to the top" of the forum list after being buried on back pages.
IMO In my Opinion-- variations IMHO=In my humble opinion-- IMNSHO=In my not so humble opinion.
Sock sockpuppet, nic-switcher, Sybil troll, or chameleon troll= A poster who changes their username, or has many different usernames in order to say or do things the more reputable, primary username wouldn't say or do. Also to make the main user's argument seem more supported ( by replying to oneself) Or to continue posting once one User account has been banned from a forum.
TTFN
HTH
HAND