People who don't believe you're a Veteran?

Okay, a bit of an odd post. I have USMC license plates, Veteran designation on my Drivers License, and my VHIC card. On top of all of that, I've a moto "Semper Fidelis" tattoo.

Yet, some people literally cannot believe I'm a Veteran. It's weird af. It's like they get visibly angry seeing me wear a Marine shirt, or when I drive my car? Namely this happens at a gym I frequent, thinking about changing gyms anyway. Mind you it's almost always other guys, and it spans ages, backgrounds, etc.

Has anyone dealt with this before?