Many people have a strong negative reaction to seeing dogs humping. They interpret it as a sign of sexual aggression. And if its their own dog doing the humping, they feel embarrassed by it, as if its somehow a reflection on them. They start yelling at their pet and trying to pull it off the other dog, which backfires because dogs like attention - even negative attention - and your strong reaction could only prove positive reinforcement for the behavior. So what should you do?