1. A really long acronym used in mocking the use of other acronyms or 1337 speak.
2. A very extreme way of saying "what the fuck?"
The acronym was crafted in the same chatroom that brought us such words as bikeyorph and beese. It was an attempt to make a ridiculously long acronym to mock others' use of acronyms. The first part of it stands for "Rolling On The Floor Laughing My God Damn Motherfucking Ass Off Peeing In My Pants Choking On My Food Shitting Myself Laughing Out Loud Oh My God What The Fuck Barbecue". The next part, WMATAGAUGH, was someone's response to the first part, an accidental mispelling of WMATAGMOAGH (Washington Metro Area Transit Authority General Manager Oren A. G. Hirsch).
Person A: WTF
Person B: lol
Person C: OMGWTF! LOL
Person D: ROTFLMGDMFAOPIMPCOMFSMLOLOMGWTFBBQWMATAGAUGH!!!
Person A: they went to change positions, and he fell over and landed on his dick
Person B: ROTFLMGDMFAOPIMPCOMFSMLOLOMGWTFBBQWMATAGAUGH!!!