I'll start. Limit one per customer.

Yo mama so black, I looked at her and thought I was asleep.

Yo mama so fat, before God said "let their be light", he said "move yo fat ass outta the way!"

- N

Yo mama so nasty, she gets sourdough yeast infections.

Your mother had sex with your father. Ahahaha! What a slut!!

Jesus Roman. This is a serious thread.

Yo mama's so dirty she has to sneak up on bath water.

Yo mama so stupid, she saw a bus full of white people and yelled "STOP MAH TWINKIE!!"

How about Yo Papa jokes?

Yo papa so hairy, he got breadcrumbs in his chest hair a year ago and a forest of mold grew. Naystee!

EDIT: I'm working on it...