Yo Mama's Halloween Fail

Alright, listen up, buttercup. This "yo mama" joke is saying your mom is so fugly that even on Halloween, when people are supposed to be scary, nobody wants to give her candy. That's how ugly she is. She's basically the troll under the bridge, but instead of charging tolls, she's just bumming candy and getting denied. And based on how you asked me to explain it, you aren't getting any candy either, chump.