What annoys me about this statement is that it's a hasty generalization. The speaker completely assumes that teenage boys are disrespectful, recalcitrant, and resistant to any semblance of obedience. Given that he is talking about me, I find it rude of him to judge my character without ever seeing me; to condemn my behavior just because he knows I'm 18 years old.
Maybe the sad thing in all this is that our culture expects this behavior. The standard for teenage boys right now is in the gutter. They are not relied on to do chores around the house, obey the first time, listen, and stay out of trouble. In fact, bad behavior is expected of them. Is it any surprise that many act like this? (no personal experience, I assure you)
I felt like running downstairs, presenting myself in front of the man in my school clothes, and politely asking, "Do I look like I'm a youth gone astray?" I didn't of course, because it was a customer. Though, funnily enough, if what he had said was true I probably would have been bold and rude enough to do it.
A semi-related comic to make you laugh:
