LOL - ell oh ell
ROFL - ARE OH EFF ELL
OMG - oh em gee
It has also been known that WTF has been pronounced like "wuh-tff" when people try say it like it's spelled, as they would say "Lawl" or "Rawffle" in lieu of LOL or ROFL.
Timmy: What the crap was that? OMGHI2U81607861048 is using headshot scripts! No fair! A headshot through the wall with an AWP is impossible!
Johnny: OH EM GEE DUBBA YEW TEE EFF??!! Ohnoes! We better report him to the admin so he gets b4nnz0r3d! Timmy, STFU and play.
Timmy: Ohnoes! I got pwnz0r3d!