The term 'Chins' was coined by the pill heads of Weston-S-Mare, a small town in the south west of England.
The name comes from the erratic movement of one's chin when on pills. a Chin being 1 pill, chins as in many pills
someone who cannot handle getting hit in a fight very well is said to have a weak chin or a glass jaw. someone who can handle lots of abuse is said to have a strong chin.
dude 2: yeah, but he's still fighting, look at him, it's like the punches aren't even affecting him.
dude 1: he's got a hell of a chin on him, that's for sure.