A "stanky-bootay" is a smelly ass or an ass that stinks from not having been washed recently.
I smell stanky-bootay" means "I smell ass.
A "stanky booty" means a "stinky ass." A stanky booty is an ass that hasn't been washed recently, and therefore it smells of doody, or poop. And ass perspiration only adds to, or increases the funk!
Please note that one can pronounce the word "booty" as "boo-tay," for an added touch of refinement, or a mark of personal distinction by the speaker.
You have a "stanky-booty" (or boo-tay).
I ain't even tryin' to smell no "stanky-booty" (or boo-tay), y'all!
Boo-tay" is a noun that means "ass.
You have a big boo-tay" means "You have a big ass.