The correct response is "Great, I'm glad I'm a paying passenger then!" said with a friendly smile. Being livid, well, just shows your age and helps validate his comments, however rude they were, about younger passengers in J/F. And what other people said about measuring your worth by what cabin you're in...

That said, I think the only time I've ever gotten a look was on an intra-European C class flight on AF. (You know, the ones where they just block off the middles of a few rows of coach. Makes US domestic F look nice!) Mid 20s, usually fly in jeans and a t-shirt or polo with a messenger bag for my laptop, sometimes looking a bit scruffy. It's all in your attitude towards your fellow passengers and the cabin crew as to how you are perceived, especially if others are prejudiced for whatever reason as in your example.

What has happened to me more than once was being initially denied use of an elite check-in line that I probably would have had no problem walking up to if I was clean-shaven and wearing a suit. Just a friendly "Yeah, I'm flying business/first today" or "I'm in coach, but I'm a Delta medallion" sorts that out. The one bad instance was in SCL about a week ago—after the friendly DL agent blocking the line asked if I was in business class, which I told him I was, he asked to see my itinerary, which I didn't have. Then he asked me WHY I didn't have my itinerary. (I knew my record locator if there was some problem, though I do try to always carry a printed itinerary for international travel.) By that time I'd pulled out my Delta GM card which appeased him.