How do some straight people "know" that being gay is a choice?

What ever happened to the phrase, "You never know until you try?" I'm curious, because I believe I can apply that phrase in a useful, alternative context; you don't know if it's a choice unless YOU ARE GAY. Now first of all, I am not saying there is some way that someone can just "try" being gay when they're really straight. That doesn't work. Gay people are the ones who should know if being gay is a choice, and I think it's pretty clear that it is not, unless of course the people who are saying it is a choice are in fact gay and in denial. That's pretty unlikely though. What is a choice, on the other hand, is whether or not to be a narrow-minded, prejudiced bigot. Hopefully, idiots who make the blatantly false statement I have referred to above will someday cease to exist. Until that time comes...you never know until you try. So shut up. Thanks.