A.S.N. variation of "fo' sho" or "fo' shizzle".
In order to make it rhyme, as is the case with "fo' shizzle my nizzle", it's often said as "fo' shankle my ankle"
We don't need to give y'all a reason, why do you care?
"So did you plow that bitch yet?"
"Yee, fo' shankle!"
A humorous descriptor for a person with extremely overt cankles.
Dude, if that girl was a dinosaur, she would be a cankleasaurus rex.