The act of ejaculating on the ribcage of an anorexic whore, and then offering her payment in the form of an apple pie.
Dude, I totally gave Susan a ribzuba last night; she was even cool enough to share the pie.
When a person plays another person's ribs with their fingers while also playing their butt like a tuba.
Cody: What instrument do you play?
Matt: I play the ribzuba, man!