No, he doesn't do it much ever, and when he does, like I said, I just yell, it's a dominance thing, males do it as do females. Let me tell you a funny story. I have a golden retriever(3 years) and a german shepherd outside. One day, when the shepherd(she's 2 now) was probably around a few mos. old, I was out walking, the neighbor lady stopped me and said you know, I just wanted to let you know in about 9 weeks, you're going to be having some little surprises..
I looked at her kind of funny..She said the golden retriever was really going to town with your shepherd. I said, well, the golden retriever has been spayed, and my shepherd is fixin to be spayed(they're both girls). So, believe me, its not just a boy thing, it's all domiance. The only one my little guy humps, even though she's close to 3 times heavier than him, is very sumbissive, and my other 2 females aren't..