How To Play The Penis Game

We have a boy. He loves his wang. He has recently started to belt out  "Penis" for no reason and out of the blue. This is how we play:

He randomly says "Penis". We could be eating breakfast, tying his shoe, playing trains at grandmas, whatever. You have to say "books" or "carpet" or "zipper". It's extremely hard not to say "vagina". 

See, this is not a game I want to play or that we have taught him about. It's anti-playing. He belts out "penis" and very quickly we have to reply with a word that has nothing to do with penis. A word to change the subject, to essentially kill the penis. It's hard. 

When people normally play this word play game, you say a word and generally say a word that coincides with said word. Such as "peanut butter" and "cracker" or "bird" and "fly". I think "vagina" might be a popular answer when saying "penis". Well, he does it so randomly it forces my mind to jumble and it takes all I have to spurt out "wall" and not "vagina" or something worse. If I say the V word, it's over. He is in hysterics, body parts will be said and the penis will be loved all the more. 

So far we are winning. He is getting creative with answers to our words. It's actually fun. He tried it at the grocery store though. On his dads shoulders. We were surrounded by T Day shoppers. Daddy put the kabosh on our game.