I really don't think it's homosexuals in particular that do this. Of course, there are gay pride events, which means that for one day during the whole year, they have a parade down town in your city and a few clubs have "gay" nights. Various religions and ethnicities do this, too. When I lived in Philadelphia, I can recall countless times I was coming into the city by car or by bus and it was detoured by a parade -- be it for a German, Polish, Puerto Rican, Catholic, Jewish, or LDS event.
And if it's an individual who is ramming it down your throat (not literally), then the above applied, too. I remember several high school essays/class presentations/discussions that always prompted other students to talk about bias against their individuality. And, of course, religion, sexuality, race, economic background all came up and everyone tried shoving it down each others throats. It's not just in high school and, when out of one of those cornball high school discussions, it becomes kind of lame. I'm a bisexual, Atheistic, Ukanian-American who grew up in a neighborhood in Northwest Philly, but I don't go out shouting it in the streets. If I did, actually, I would look like an idiot because most of that stuff is my business, unless you care to have a discussion about religion, sexuality, nationality, economic upbringing, etc... and I use an anecdote.