If you're really good friends just say "You suck!" then tell him an even unfunnier one
"i don't get it"
Just say, "Yuk, yuk, yuk, yuk yuk."
Just say good try but that was dry. usually you may laugh because it was a fail.
If it was a good friend, I would just chuckle and tell them it wasn't very funny.
Then they're not great friends. It's a joke .. nothing to get so touchy about.