Compared to what?! Aviation is actually one of the most standard fields there is. I can't think of any other situation where 2 people, having never met, can be thrown into a situation where they have to trust each other implicitly. The only way to make that happen safely (and I think you would have a hard time arguing that aviation is unsafe) is to make sure everyone is on the same page with standardization.

I have to agree with most of the other posters here. I would hope your friend has the cajones to stand up for himself, especially when an instructor like that is so far out of line. It's amazing what people will put up with in this field all in the name of pursuing the dream. What if an econ professor in college had slapped you after handing back a midterm? Would you (or your friend) sit there and take it? Would you at least say something? Would you slap that professor back? So you want some advice for your friend? Tell him to grow a pair. You could also recommend that he run far far away from TSA.