Hurrah, a true thing in Snopes!

Agent: Hello. I would like to order nineteen large pizzas and sixty-seven cans of soda.

Pizza man: And where would you like them delivered?

Agent: To the Southwood Psychiatric Hospital.

Pizza man: To the psychiatric hospital?

Agent: That's right. I'm an FBI agent.

Pizza man: You're an FBI agent?

Agent: That's correct. Just about everybody here is.

Pizza man: And you're at the psychiatric hospital?

Agent: That's correct.

http://www.snopes2.com/humor/jokes/fbipizza.htm