Best definition
Your mother is a cankerous whore
Jack Blade quote from Tropic Thunder. His character was experiencing withdrawl from cocaine and he was tied to a tree.

Crazy shit ensued.
Basically, It means your mother sleeps with everyone and has deseases between her legs, and most likely, you are unwanted crotchspawn.

“Your mother is a cankerous whore!”

“Damn.”

“Hey, remember that time I called your mother a cankerous whore? I didn’t mean it man, she’s a nice lady.” – Tropic Thunder