Here's another one, and I hope I get it right.

A man was walking down the sidewalk in his neighborhood. He noticed a young boy dressed like a firefighter, hat, boots and all. He had his Red Ryder wagon decked out with a water hose. The man noticed that the little boy had tied his wagon to his dog, so the dog could pull his "fire engine" around. As he got closer, he could see that the little boy had tied the rope to the dog's testicles. Horrified, he asked the boy why he couldn't have tied the rope to anything else on the dog. The boy emphatically replied "but, sir, if I did that, I wouldn't have no sireeen."