An Extension of the standard ROFL. This literally means: Rolling On The Floor Laughing My Frikin Butt Off. While the speaker isn't always actually laughing, on the floor, or lacking his rear end, this is a good expression used to denote humor in another's words.

(noun) A successful type of theft which results in an acceptable, impressive and rewarding payday for the protagonist.

Or as an equally chuckle-inducing alternative: rolling on the floor laughing my fuckin balls off. Which always has that effect on me when I see it writ large in web forums. Maybe I'm just childish!

Rolling on the floor laughing my freaking butt off
a term used by young people whilst texting