My bunny has a bald spot on his butt?

could be a skin infection from a dirty cage or other bacteria. could be so nervous it made the bald spot itself from licking at that spot. you need a vet. when you clean his cage, put him in another smaller container like a box with holes in it, if you don't let it run around your room while you clean. trying to clean the cage with the rabbit in it will make him stressed.

Normal moulting should not result in baldness. I would get him checked over at the vet asap, it could be fur mites or something else entirely, to include allergies.

depending on his coat color and molting patterns it could be seasonal molt. This will grow back over the next couple weeks.

It could be a mite infection. He could be fur pulling out of boredom or stress.

Does the skin look healthy? no flaking, just pink no redness.

If unsure have your vet take a quick look see.

It may be mites or an external parasite. Go to the vet to make sure.

He's gay, and his boyfriend has terrible aim. You can only get hit so much in one spot before you start to get worn down.

That is the hole where his poop comes out of

That would be his anus, lady