If he's a sales rep who cold calls people, he's probably experienced dozens of hang ups a day in the year he's been at that job. Something must have pushed him over the edge that day. Either that, or he's done this to many other people, but this is the first time someone called him out on it.

My guess is the latter.

He could have been well-prepared. That doesn't give him the emotional maturity to deal with it. An employer's role isn't to turn a child into an adult. I can be taught about the reality of being rejected when I ask a romantic interest for a date, but in the end, my response when rejected boils down to character.

Nothing can prepare you for hang ups. But how you react to it shows your character. And if you can't handle it, find a job that doesn't require cold calling.