Shorts and a tshirt work just fine for me. Not a Bud one though, I am more of a Coors fan. Perhaps a Harley shirt instead, I've got a lot of those.
Also, let's see: Pan Am, gone. Dinosaurs, gone. Coincidence? I think not.
Let it go. If YOU want to wear a hat, go ahead. That is fine. I'm glad it makes you feel special. For those of us lucky enough to work for a company that doesn't require them, good for us, don't let it ruin your day.
In my opinion, it looks dorky and serves absolutely no function what so ever, particularly out on a flight line doing a preflight. Traditionally it is impolite for gentlemen to wear a hat indoors. So I guess the only time you should wear the thing is while you are on your way to and from the airport.
If you want to look "professional" while on the crew bus and in your car by all means have at it.
FJ