Why is showing your sexuality off so important for a lot of gay people?
I don't know why. But I think there's a difference between "showing it off" (aka flaunting) and subtly advertising it, as I sometimes do. Let me explain, as I have here before:
I would never have gay indicators on my person or vehicle after I came out, though I was out to anyone who needed to know it. Then one day I was running late for a college class, and grabbed blindly into my closet for a shirt.
After class a female student stopped me in the hallway, to thank me for being so "brave." I was puzzled, so she pointed to my polo shirt, embroidered with the words in rainbow colors "Gay Mens Chorus of Houston" a souvenir of my brief involvement with them.
She explained she felt much better, a new student on that small campus with no gay student groups, to find another gay student and someone who was not afraid to be out. I directed her to the office of the gay faculty advisor to help her network with other gay students.
Afterwards I reevaluated my decision to never display gay material, and soon had gay stuff on my car and motorcycle, and also that I wore. Small & subtle things, that likely only other gays would recognize, but to let them know they weren't alone, not to be frightened like that lesbian co-ed had been. It was for THEM, not to flaunt myself and show-off to straights.
It's also why I attend Gay Pride & parades, to give encouragement to closeted gays, and to thank the many straights who support us.
BTW, tonight my partner & I are going for cocktails and dinner with his straight sister, along with another straight woman. It won't bother my partner & me if some people assume we're 2 straight couples, so we won't be camping it up to correct them. It's not essential to us that everyone always knows we're gay, only when we ourselves choose to send the message within our own community of fellow GLBT and supporters.