Until recently, I would have said I am not a big fan of "potty humor" or fart jokes or anything like that. That said, they are extremely effective.
Like I assume many kids do, Anthony and Francis often say, "Tell me a story about Anthony the ____ and Francis the _____." Lately, they have been asking for Anthony the police officer (or sometimes bomb squad or SWAT or something), which seems normal enough, but naturally Anthony's character needs a nemesis: Francis the Bad Guy Farter.
So, their story usually goes something like this:
Anthony the bomb squad SWAT team member got a call about strange noises and smells coming from under a bush in the park. He arrived on the scene with his trusty K-9 and his bomb squad robot in his police SUV [the accessories are really important] to investigate. Suddenly, from under the bush came a sound. Do you know what sound it was? Pffffffff.
Then we all make the sound for a while. The longer it goes on, the funnier it is. Comedic genius!