RABBI BARANS: Ugh, I can’t even look at this mayonnaise.
A joke based on the stereotype that Jewish people hate mayonnaise, preferring mustard as their condiment of choice. It has nothing to do with mayonnaise not being kosher – there’s no religious stipulation against it.
Jewish comedian Milton Berle once cracked, “Anytime somebody orders a corned beef sandwich on white bread with mayonnaise, somewhere in the world, a Jew dies” – I guess, dies in horror? Although Milton Berle himself ate mayonnaise on his corned beef sandwiches, making fun of people eating mayonnaise became a staple of Jewish comedy.
The Annotated Gilmore Girls 