There has been great debate on here recently about what is considered a Glass Jaw and what is considered an Iron Chin. There seems to be a wide disparity on each when it comes to opinion(s) on this subject. What are your credentials for a fighter having: A Glass Jaw and An Iron Chin Thoughts?
Yawn. Amir Khan has a Glass Jaw, James Toney has an Iron Chin. That's about as simple and clear a distinction as there can be I think.
Not true. There are several examples in history of true Iron Chins never having been cracked. The term has been watered down, but a true Iron Chin does not break. It is Iron.
Fighters with glass jaws get knocked out cold multiple times (think Hasim Rahman) or starched brutally by light hitters (Fraudley, for example). Guys with iron chins take every punch that's thrown their way and keep coming - they are rarely, if ever, knocked down.