As another young-ish traveler (now 27 but been traveling for work for years and still look on young side) this stuff happens but definitely worth a comment. I've never had anything that blatant. I was surprised when traveling in F from LAX-JFK nobody actually questioned me more at Flagship check-in, FL, and the FA treated me just as well as the celebrity across the aisle! All while wearing comfy cheap jeans, a casual tshirt, and flip flops!

I actually find it's fellow travelers that I get that more from - countless times when waiting to board first class men in suits have been at my side saying "excuse me I'm in first class" and trying to go by. And I just give them a big smile and a "me too!". They always look very sheepish but I'm just lucky enough to not have to travel in my professional clothes.