I know where you are coming from. I think I know what the cause of it is too. You see, when we got a boy dog and neuterd him, him humped everything he saw. It is because, when they have that cord cut it makes them feel like something is missing and makes them ( sorry to use this word) horny. He then has an urge to hump every other dog and person. It is the horny part that causes this. Also, if it has been a while since he has been neuterd, it is probably because he smells a female in heat and cannot get out to go see her. That can drive a male dog nuts and he will definately start humping everything in sight. I hope that this helps.