An example: I have no problem with gay people, I have a ton of gay friends and spent a year living with a (really cool) gay couple. But what I absolutely cannot stand is people who turn everything into a statement about them being gay. Who try to force me to acknowledge it and use it as an excuse for sucking in general. No, I couldn't give less of a fuck about your sexual preference. But don't try to make it an issues when it's not.
PS: On sexual discrimination: If I'm attracted to a girl, I might flirt with her and see how it goes. If I'm at a party, I may try to hook up with a girl. I don't do it with co-workers because it'd complicate the workplace—but otherwise why not? Since when has it become wrong and inappropriate to hit on a girl…?