I think that we are all partly responsible for your friend being so flamboyantly gay--indirectly at least. Having observed this, and put some thought into it, I think that the outwardly overt homosexual is partly a product of societal repression and partly just the result of having a different hormonal makeup than what is typical of a straight person. If you think about it, homosexuals have been essentially vilified and told that they "aren't people" for ages, and because of that I think that the flamboyancy is a sort of identification method. Imagine being bombarded with images from television, other media and your own home environment telling you that you have to act "THIS" certain way, that being attracted to girls is what is normal and what is right, while in your heart you know that you feel differently.
While I am not gay, I still know that that would tear me apart. It's kind of like... a way to have some sort of community, some sort of way of identifying yourself as a person; I believe that gays have been almost... pushed into a corner, so that they almost have to act out in order to be seen in a different light--to separate themselves from society around them. Also kind of as a means of creating a subculture in which they can relate to others similar to them. I really don't know for sure though, I could be completely wrong and off base. It just bugs me when people honestly question whether or not being gay is a choice or not. Why are you attracted to a certain type of girl? Why do you have a particular fondness for a type of food, or a certain scent? You don't know, you just like it--it's innate. I agree that some of those things can be affected by past experiences or emotions tied to those examples but, they are still a product of yourself--your own natural genetic makeup.
Imagine a sculptor and his/her stone: as a person, you are given certain specific traits and characteristics via your parents genes + your own little twist as a person (yes, I know I'm being highly scientific)--this is the material that the sculptor begins with. As you progress through life and experience it's ups and downs you are changed and formed into a more complete person, but your base material (your self), remains unchanged. Basically, while outside factors and your environment shape who you are, certain things are not choices and you have what you are given: i.e. your sexuality.