How about some 'doctor' ones? They are popular with my 2 (6 and 9). Eg."Doctor, doctor, I've got a sore throat." " Go and stick your tongue out out of the window." "Will that cure my sore throat?" "No, I just don't like the man opposite."
"Doctor, doctor, I think I'm invisible." "Next, please."
Or that old favourite: "Waiter, what's that fly doing in my soup?" "I don't know, sir, but it looks like the breaststroke."
DS2, also 6, really likes this one, but it is a bit longer:
"A man is walking down the road with a penguin. A policeman sees him and says "You'd better take that penguin to the zoo." "OK, I will," says the man. But the next day the policeman sees the same man with the same penguin. "Hey," he says, "I thought I told you to take that penguin to the zoo." "I did," replies the man, "and I'm taking him to the cinema today."