Well, I've seen men do it with women as well, it seems very arrogant that they think every woman or man wants to get in their pants.
It's to do with they think they're awesome the best in the world and everyone loves them which isn't true there ego's are too big
Arrogance really, lack of understanding... P.s seriously, you could make like a whole album out of all these one worded threads
There's a possibility that they don't know many gay people and they are just going by what they have been told or heard about the gay community. Once you become older, or as more people come out they will realize that it's just a big misconception.
Insecurity. They feel as if any slight slip-up of their character will result in eternal shame and being labelled as gay/effeminate. They'll either mature soon or turn into slightly more terrifying men with massive masculinity issues, but it should get better as you get a little older.
People are simply idiots- that's the truth really. I'd say it's a combination of ignorance, egoism, and idiocy. Ignorance because they probably know nothing about different subcultures of society: LGBT, the other sex's point of view, etc. Egoism because they think they are the best. And Idiocy for being ignorant and egotistic