2 groups:

The most common way to get "the funny" is to counter point 2 distinctly different groups. In this example we will use Jews and the Taliban.

A Taliban militant gets lost and is wandering around the desert looking for water. He finally arrives at a store run by a Jew and asks for water.

The Jewish vendor tells him he doesn't have any water but can gladly sell him a tie. The Taliban begins to curse and yell at the Jewish storeowner. The Jew, unmoved, offers the rude militant an idea: Beyond the hill, there is a restaurant; they can sell you water.

The Taliban keeps cursing and finally leaves toward the hill. An hour later he's back at the tie store. He walks in and tells the merchant: "Your brother tells me I need a tie to get into the restaurant."