At least I have a mom, not two dads and a hole in the wall
I swear someone said this to me as a comeback to a "your momma" joke but to this day I have no clue what he meant...
written by an*nymou* user, approved by Log

Ah yes. I've heard this one, and I'm across the bloody ocean. I think it meant that one dad buggered the other, and the other buggered the wall, which then became pregnant. Variations included two dads, a water buffalo, and a hole in the wall. The hole was also replaceable with an electric socket.
written by excluded pupil, approved by Susan

I'm more inclined to think that this is a reference to the gay phenomenon of glory holes, where gay man stick their willies through holes in toilet walls and another man hops on in whatever fashion he fancies. Sometimes there are drawings around glory holes that make it look like your willy is an anteater's nose. This isn't very erotic for the man who is sucking it off, so he might put his bum on it instead.
This is how I understand glory holes, by Log.
written by Jo* B*yth, approved by Log