It's internet Macro speak for when you want somebody to cum on your butthole or imply that somebody is enough of a fag to want your cum on their butthole.
When something is so funny that you choke on your metaphorical bread. Can also be amalgamated with lmao and rofl.
(Roflcomblmao = rolling on the floor laughing choking on my bread laughing my ass off)
Dan: Yeah! Roflcomb!!
That kid is a fag, he must be a COMBS!