I usually pretend to be straight by omitting who I'm attracted to or pretending to like boys. This works pretty well in real life, but it makes me feel invalidated about my sexuality. On the internet I do the same thing in reverse. People assume I'm a straight male when I talk about girls and I never bother to correct them. I sometimes even call myself a straight male. It feels good.
I personally act as if I wasn't interested. When someone asks me why I'm still single (I've had girlfriends before) I just say that "I have enough problems already". It still feels like lying, even more when they talk about me having kids... But well, at least I don't have to pretend that I'd like to date a girl.
If a girl asks me why don't I have a girl friend or comments that I should get one my response is "do you volunteer?" If a guy asks I say that I have personal problems I need to sort out before seeing anyone which is true. If someone asks directly about my sexuality then I answer truthfully.
You could; "Mum, Dad [or whoever] ... I'm straight" and then when they say "really?" say "No, fooled you, I'm [fill in]"
It really depends how far I want to get into it. If someone new mentions girls or a girlfriend, if I get the feeling they may not be down with the rainbow swirl, I say nothing and just go with it. Beyond that, it's usually just easier to tell people I'm gay.
I guess I was in denial about my gayness in high school. But when asked about boyfriends I always did the "Oh I have a boyfriend who lives in such and such state". Maybe having long distance boyfriends helped me think I was straight without having to have sex with men.
