Sports are different. while I don't care much for sports, that's actually got a purpose and people have a reason for supporting their favorite team.
with gays, that's just being annoying. we get it, you're gay. keep it to yourself. not everyone has to know your sexuality. do you see that many straight people using a flag of their own? definitely not as much, i can tell you that for free.
Quick rant here: Me personally, I couldn't care less if you're gay or not. But saying your gay as the first thing to someone or using it as a conversation starter, that ticks me off. It's even more annoying if you're trying to give someone an eyesore with the clothing your wearing. Gay people and bi people in general? I'm okay with until they say or do the wrong thing. Hell, I'm dating someone who's asexual, and not ONCE has she brought up lgbbq. She's pretty, she's honest, and it was only one time when she told me she was asexual. I didn't care, I still love her. Lets use that as an example real quick: You're having a normal conversation with someone, you have no idea they're gay. I'll say something after time has passed like "So, you find someone yet?" and they could respond with "Yeah, my boyfriend Alex." I wouldn't mind them being gay because they're a normal person who gave me an appropriate answer. Now, lets change the situation a bit: I'm chilling with this other guy having a conversation, and I'll ask the same question. If he were to respond with "Oh, I'm gay." then I'd be a little annoyed, but not enough to just stand up and walk away.
Now if I said one word to them like "Hello" and they immediately say "I have a boyfriend" or "I'm gay", then you can bet your ass that I'm either gonna stand up and walk in the other direction, or that I'm gonna start ranting on and on about how dumb it is to start a conversation like that.
Now that that's out of the way, lemme sum this up for you in case you aren't gonna read all this: If you're gay, okay. Nobody will give you a hi-five or congratulate you. You'll only annoy a lot of people. Just act like a normal human, speak to other people like a normal human, and for f**ks sake, don't ever talk to me about transgender or I will leave you on the floor with a broken nose.