Someone who uses the bathroom for too long, or someone who uses the bathroom and doesn't clean up after themselves.
Kelly: Man, Fred was such a bath-hole tonight! I was waiting outside the bathroom for sooo long, I thought I might've shat all over the hallway! And when he did finally come out, he didn't even light a match!
Todd: Oh, man it's on! I'm gonna feck that mofo up, yo.