that fits the following pattern:
Yo momma is so [derogator attribute], she ....
- Yo momma is so poor she can't afford to pay attention.
- Yo momma is so nasty she made Right Guard turn left.
- Yo momma is so ugly, when she goes into a bank they turn the security cameras off.
- Yo momma is so dumb it takes her 2 hours to watch 60 Minutes.
The genre is so big that Google
even has a single page dedicated to sites with Yo Momma jokes (Recreation > Humor > Jokes > Yo Momma Jokes).