Dackface
A person who lets someone else go down on them. You can also say 'to dack' which means to go down on someone. It's a super rude way to call someone a dackface.
You're a dackface, I've seen uglier things on the sidewalk.
Why are you still talking to him? He's a dackface and you know it.
Don't let your sister near him, he's a dackface and she'll get sick.