What do you do if your gay friend likes you?

If your gay friend knows that you are not gay, then they should respect your decision to be straight and not put this type of pressure on you. Sometimes people are attracted to what they can't have. And sometimes they can rationalize things like "we are already friends and this person knows who i really am and doesn't have a problem with it" into "maybe we can be more". At this point, you will have to decide what to do. Sometimes you have to end friendships that cross the line. Sometimes you simply have to tell the other person how you feel. His/her feelings may be hurt, but they will get over it and the friendship can continue.