I gained EBG status when I was 21 and did my first flight in C when I was only 18.
So the "stare part" is something I have experienced many many times and stopped caring about after a while.

I think the best thing to do is to stand firm of what you are entitled to while at the same time being polite and respectful towards the staff, and hopefully they behave the same way in return.
On a good day you might even get something extra in return for handling their "mistake" in a professional manner.

I always try to dress neatly when travelling though, not overdressed (unless I have to), but I'll leave the shorts in my suitcase.
If you travel longhaul or during the night you can always change to something more comfortable on the plane.