ROFLCL is a compound acronym combining ROFL, Rolling On Floor Laughing, and FLCL, Fooly Cooly, an anime.
It is a tack-on statement to ROFL that supports the fact that the one speaking is both an internet user and anime watcher. It is used as a statement by itself, like ROFL, or can also be used as an adjective (see example).
"<insert witty joke here>"
"Did you see the AMVs at the kon?"
"Yeah, they were totally ROFLCL!"
The rapid body movement of a Halo player after swinging a locked-on Energy Sword. The movement often causes much frustration to other players (namely those who were minding their own business 20 feet away), and therefore a terminology of the word was invented.
Player 1: *pulls out the Energy Sword*
Player 2: Come on, dude, not the rocketskates again!