A gentleman was standing on a street corner with his 5 year old son waiting for the light to turn red so they could cross. The man notices that accross the street, directly in front of them, there are two dogs fornicating. He was hoping his son wouldn't notice because he was not yet ready for the lecture on the birds and the bees.
But, sure enough, his son sees the two dogs fornicating and asks his Dad - "Daddy, what are those doggies doing?"
The man thinks quickly and, presto, comes up with what he thinks is a viable explanation: "Well, son, you see the doggie on top broke his leg and the doggie on the bottom is being a good samaritan and is helping him get to the hospital."
Just when he thought he got away with it because his son had not questioned the explanation, the son speaks up - "You see Dad, just goes to show you - you try to be a nice guy and help somebody and they screw you right up the ars.