So, I told him a leper joke.

"Did you hear about the leper hockey game? They had a face off in the corner".

He laughed pretty hard, and asked for another. I told several more leper jokes, and he laughed like crazy after every one.

Then he said, "Do you have any more animal jokes?" 

I said, "Animal jokes?" 

"Yes, like the lepard ones". 

It turns out that he had never heard of a leper.