A "Your Mama" joke is an insult directed at another person's mother. Although these kind of insults tend to be demeaning, they are generally considered to be tongue-in-cheek and meant to be viewed as light-hearted in nature.
The modern "Yo Mama" joke has been around, in one form or another, for hundreds of years in literature. Examples of this can be found all the way back in the works of Shakespeare, notably in the play "Timon of Athens." The "Yo Mama" joke enjoyed heightened cultural popularity in 2006 and 2007, when MTV aired a show centered around making the jokes in a competitive setting.
The first documented joke about a person's mother was found on tablets carved in ancient Babylon over 3,500 years ago. Archaeologist J.J. van Dijk found the original tablet in 1976. The stone contained six riddles, and while some things are probably lost in translation, one of the riddles included the words "beer," "sexual intercourse" and "your mother."
"Yo' mama is so fat, her belly button gets home 15 minutes before she does" and "Yo' mama so ugly, people go as her for Halloween" are some yo' mama jokes. Another is "Yo' mama is so fat, I took a picture of her last Christmas and it's still printing."