This was my absolute favourite joke as a kid. I started telling it to Jason one day, and to my horror, not only had he not heard it before, but I couldn't remember how it went exactly!
So after a thorough Google search, I finally found a similar version, and then modified it for you benefit, so here it is:
Three kids, Trouble, Manners and Shut-Up, decided to play a game of hide-n-go-seek together.
Trouble was it, so while he counted Manners hid up a tree and Shut-up hid behind a police car.
When the policeman noticed Shut-up hiding behind his car, so asked him, "What's your name, kid?"
"Shut-up", answered Shut-up.
The policeman was appalled, "Excuse me?!", he said.
"I said Shut up.", Shut-up replied.
"Where are your manners, boy?", the policeman exclaimed.
"He's up a tree", Shut-up said.
"Are you looking for trouble?", the policeman asked.
To which Shut-up replied, "No, Trouble's looking for me!"