When you've fingered a girl on her period, gotten blood on your fingers, and the proceed to finger her in her ass and getting shit on your fingers. Barbeque fingers.
Dude, i fingerbanged this chick in both holes, got them barbeque fingers now you feel me?
When you finger a girl's asshole and some sort of residue comes out onto your hand. You decide to give it a lick, it looks like barbecue sauce. It's definitely not.