hey dude dont let people get to you. If you know you are straight they can think what they want. I have a friend who has a camp demeanor, fashion sense and voice and naturally we all call him gay (much like yourself) but unlike yourself he plays along with it and he says things like "im the gayest straight man ever".Link_to_Future said:TLDR
the best advice i can give you is just give yourself a bit more authority, simple as that. You dont have to change how you dress or how you act but you need to be confident in who you are or people will assume you are hiding something (e.g homosexuality). Just stand up tall and first of all accept who you are and then learn to be more dominant and stand up for yourself (not in an aggressive manner though)
edit: theres the time honoured classic of "are you gay?"...."are you asking me out?" thats bound to shut them up