Its always been my impression that anyone who feels self-conscious about being straight around gay or bi people is either closeted or probably suffering from some kind of social anxiety. I'm aware there are some predators out there that get off on targeting straight people who have exactly that kind of anxiety, but I find its a lot easier to just say "Eh, you're not really my type." if someone from the same sex shows you a little too much attention. It sidesteps the whole issue and avoids burning any bridges. If they keep it up after that or get aggressive, you're dealing with a real freak and you need to get the fuck out of there.
Though as a rule I also just avoid anyone who gets euphoric about their sexuality and overuses terms like "liberating" and "I can just feel good being me!" is worth avoiding in the first place. Those types are just as irritating to be around regardless of their sexuality.