A person so experienced at being class clown that hopelessly unfunny students come to him for advice.
Bob: Dude wanna come to my house?
Jimmy: Nah I have an appointment with my class clownician.
Bob: How much is he asking?
Jimmy: It's 10 bucks an hour, but if you tell a good joke at the end of the session he'll only charge you five.
Bob: But you suck at telling jokes.
Jimmy: I know. For me he usually charges an additional fee.