I don't get it...
Two mathematicians, Joe and Richard, were having dinner in a restaurant
in Portland, Oregon, arguing about the average mathematical knowledge of
the American public.  Richard claimed that this average was woefully
inadequate while Joe maintained that it was surprisingly high.

"I'll tell you what," said Richard, "when I get back from the bathroom
we'll ask our waitress a simple calculus question.  If she gets it
right, I'll pick up dinner.  If not, you do.  Okay?"  They agreed, but
once he'd left, Joe called the waitress over.

"When my friend comes back," he told her, "he's going to ask you a
question; you should respond 'one third x cubed' no matter what the
question is; got that?  There's five bucks in it for you."  She happily
agreed to the gag.

Richard returned from the men's room and called the waitress over.  "The
food was wonderful," he started, "incidentally, do you know what the
integral of x squared is?"

The waitress looked startled, then pensive, almost pained.  She looked
around the room, at her feet, made gurgling noises, (Joe was starting to
sweat) and finally said, "um, one third x cubed?"

Joe beamed in relief as an astonished Richard paid the check and an
irritated waitress muttered under her breath, "...plus a constant."