Donut Hole

Yo mamma is so stupid, she returned a donut because it had a hole in it.

Explanation

Explain Bear

Hey, genius! Explain bear here. This "yo mamma" joke is playing on the stereotype of "yo mamma" being incredibly dumb. The humor comes from the idea that someone is so stupid that they would complain about a donut having a hole, which is, like, the definition of a donut. You probably returned donuts, didn't you?