Well, he didn't do it to all the monsters. Just the mannequins and the spitters who looked like they were in straighjackets. Not the doormen, which would have been weird, since they walked on four legs. It almost looked like a dog. Which quite frankly, ew.
I don't know what that says about him, but at least he didn't try to hump any humans while I was there. In which case, I would have had to stop him. Possibly.