I think we can all agree nobody especially wants a "yo mama" joke told about her, what with the undercurrent of misogyny inherent in that. But of course, playing the dozens has a rich history, and not solely in African-American culture—the Wikipedia article on it is an interesting read. The Norse, Arabic poetry, 16th century Scottish poetry, Shakespeare's era—many examples of insult competitions.
Having not grown up immersed in any of the aforementioned cultures, I was caught off guard this afternoon when Ben trotted over to me at the school playground. "See that boy over there? He said you're a peabrain."
"Meaning you're a peabrain or I am?" I asked.
Alas, it did not occur to me until later that I ought to have advised Ben to concoct another insult in return. I told him the other kid was playing a "yo mama" game wherein you trade insults and try to top one another. He came up with "Yo mama lives in the sewer," which I thought was an excellent first attempt.
Now he will be ready for the next round. I can't wait!