It can be something said after a "your mom" joke, but that doesn't mean it isn't true.
And it hurts more when your friend thinks that your just trying to make a comeback, and keeps going...
Jeff: Does your mom want her underwear washed with bleach or without?
Carl: My mom is dead.
Jeff: Should I wash the body, too?
Carl: *beats the shit out of Jeff*
Something used after a yo mama joke, not only to make them feel like crap, but also to ruin everyones fun.
Joe-Yo mama is so poor, she goes to Kentucky fry chicken's to lick other people's fingers.
Chris-My mom is dead...
Joe-*looks sadly at Chris*
It is the most common comeback against a Yo Mama joke. Used in an emergency when one can't think of anything to say. Using it automatically results in Fail for being such a lulzkiller. Please note that this is NOT the ultimate comeback
Bob: Btw, can you get my wallet for me? I left it on your mom's dresser.
Drew: My mom is dead
Bob: That explains why she wasn't screaming so much