My girlfriend's sister and brother-in-law have a Shih Tzu named Bonjoo who has recently developed a fondness for humping Terry, my girlfriend's Golden Retriever, despite the fact that they're both neutered males. Here Bonjoo demonstrates the classic leg-humping technique normally executed on human legs.
Bonjoo goes to town on Terry's lower spine.
Bonjoo can get away with this perverse rapage because Terry's being a Golden Retriever makes him a laidback, easygoing dude. Even when he finally gets pissed, all he does is deliver a harmless bite, which Bonjoo probably misinterprets as a love nibble.