Yo mama is so ugly, when she got raped, the rapist was the one getting PTSD!
Yo Mama's Traumatic Ugliness
Explanation
Explain Bear
Listen up, genius. This "yo mama" joke is saying the mama is so ugly that even a rapist would be traumatized by the experience. It's like, her ugliness is so extreme it causes psychological damage. Also, you need to brush your teeth, I can smell your breath from here!