Yum Kippur.
Explanation: This joke plays on the similarity in sound between “Yom” in “Yom Kippur,” a Jewish holiday, and “Yum,” which is an expression used to describe something tasty. The humor lies in suggesting that instead of focusing on the solemnity and fasting of Yom Kippur, people are thinking about food, thus celebrating “Yum Kippur” before and after the fast.