Completely off the specific topic (it would fit more in a general thread about "insult songs"), but if anyone is interested in exploring a wider or cross-cultural perspective...

I just recently posted a VIDEO of a performance (staged, unfortunately) of a sort of "Yo mama" in Punjabi culture (India). Often however, the target is "your daddy". Insults with "your mama" are indeed there in the culture, but those are usually just to be nasty in a sexual way. The kind of insults here (more like disses or "dozens") tend to insult the father or other males or else people who otherwise represent the implied inferior social status of the "people" to which the insulted person belongs.

It begs the question (posed by Azizi earlier) of "why Mama?", as well as the question of why talking about someone's mom is interpreted as "fighting words" in lots of societies. What "function" does it serve (if any)? As for the Punjabi example, my video notes give an idea of the function in that context:

At weddings, the bride's family and guests, especially her father, are put in an "inferior" position to that of the groom's people. In this context, it is the "right" of women from the bride's people to cut down their superiors with mild insults in the form of these songs. The father of the groom is a particular target. It gives a way to ease some of the tension and let them blow off frustration since, after all, they're not REALLY insulting, right? -- they're just singing songs!