How do I stop my roommate from saying weird things?

He will come up to me and say "sing about a puppy" we don't have a dog. When we are watching TV he says" would you Her"? referring to a woman on TV and then all through the program he will say "HER" HER every time a chick is on the screen asking me if I would sleep with her. Through the day he keeps asking me."what song you gonna sing. I keep telling him to stop and he does for about five minuets and starts again. WHAT SHOULD I DO?