IBTL = In Before The Lock
It's common on flame-ridden forums
Personally, I avoid sarcasm issues by using a l33t-esque style with deliberate mispellings, 'OMGOMG's, and lots of ones and exclamation points at the end.
I.E. "OMGOMG g4ez r teh 3b1l!!!!11111111111111111"
Obvious cues not to take it serously