Of course they exist. Some guys simply can't take a shot, that means they've a glass chin. Khan is rocked to his boots practically every time he is hit clean, even by guys who arn't hitters, this means he has a glass chin. Guys like Froch are the opposite, they have to be hit with pitch perfect bombs to go down.
Glass chins? A fighter can take two hundred punches in one fight and get knocked out in round one the next fight. It dont make sense to discuss it. You can say some fighters has a granite chin but Like Tyson did he knew where to hit his opponent.
They do exist in that some guys have much better punch resistance than others, but the idea that anyone who gets knocked out, or knocked down, or staggered, or pushed back has a glass jaw is silly and overstated.
