While reading newsgroup articles or messages on some message board, it's more than possible that you'll encounter a strange acronym. Most of them are acronyms for english statements, but while browsing local (regional) groups/boards you might encounter even local ones. Below are some of most common acronyms used to day, you might want to use web search if you'll ever encounter others.
afair as far as i remember
afaik as far as i know
brb be right back
bbiaf be back in a flash
bbl be back later
np no problem
no no offends
hth hope this helps
fyi for your information
imho in my humble opinion
lol laughing out loud
j/k just kidding
re hi again
Re: response/reply (actually: In Res)
wb welcome back
wtf what the fuck
OT offtopic
EOT end of thread/topic
rtfm read the fine manual
rotfl rolling on the floor laughing
cu(l8r) See You (Later)
ymmv your mileage may vary
ntg nie ta grupa (wrong group)
ztcw z tego co wiem (as far as I know)
mspanc mogłem się powstrzymać ale nie chciałem (I could resist but didn't want to)
nmsp nie mogłem się powstrzymać (I couldn't resist [myself])
*Plonk* that is actually a sound of someone falling into a spammers/trolls well (means that someone is not reading other party's messages anymore)