[Theoria]

Sorry, but I was taught to remove your cap when inside a house or building. I see the opposite today, as in your photo.

[Errant]

Well, certainly you do in some buildings and when you sit down to eat, depending again on where you’re at or if you’re military. We cap wearers are not without etiquette.

[Errant]

Btw, the gentleman in the photo is a comedian, and the cap is part of his shtick. You should check him out, as I'm sure you'd fine his repertoire enlightening. Youtube, "Larry the Cable Guy". :)