the beauty of this insult is that it is a double entendre and it can be taken in twodifferent ways. you could either tell your friends that they have "yo momma disease" or you could say that their mom is a disease.
Jack: dawg can i get some help over here
Aidan: yo momma disease (your mom a disease)
Jack: My mom's a disease
Aidan: no, yo momma disease.
Jack: :(