The story
Alteration of antidentist, from anti- + dentist, to rhyme with anti-Semite. Coined in an episode of the American sitcom Seinfeld, in which Jerry Seinfeld is annoyed with his dentist, Tim Whatley, who has apparently converted to Judaism only because he wants to be able to tell Jewish jokes. Kramer calls Jerry an “antidentite” in response to Jerry taking offense to Whatley's Jewish jokes.
Etymology from Wiktionary, CC BY-SA 4.0.