Yo momma jokes are textual memes referencing a certain aspect of one’s mother, such as her obesity, ugliness, stupidity, etc., and compares it to an outrageous event proving the aforementioned quality. Yo momma jokes have been floating around in the interwebs for quite a while, though their origins most likely trace back to the African-American oral tradition of “playing the dozens,” in which, according to Wikipedia, “two competitors, usually males, go head-to-head in a improvised competition of often good-natured, ribald trash talk. They take turns insulting… one another, their adversary’s mother or other family member until one of them has no comeback.”

According to Wikipedia, "The classic ‘Your mother’ joke is a snowclone of the form: “Your mother is so X she’s Y”, in which “fat”, “stupid”, “ugly”, etc. are substituted for X and Y." Also, the article mentions that “yo momma” can also “take the form of a metaphor.”

Examples:

Yo momma so fat she got baptized at Sea World.

Yo momma so fat she stood on the scales and it said “one at a time”!

Yo momma so ugly she makes onions cry.

Yo momma so stupid she sat on the TV and watched the sofa!

Yo momma so stupid she starved to death in a supermarket!

Yo momma so stupid she tried to alphabetize a bag of M&M’s.

Yo momma so poor the burglars break in and leave money.

Yo momma so dirty she turned the local swimming baths into the Dead Sea.

Yo momma so scary she frightens the cockroaches away.

Yo momma so old she owes Fred Flintstone a food stamp.

Yo momma’s like a chewing gum machine – 5 cents per blow.

Yo momma’s like a bowling ball – she gets fingered, chucked in the gutter and still comes back for more!

Yo momma’s like The Titanic – she’s guaranteed to go down on the first date!