One of my friends kept asking me how I know that I'm bisexual (*) given that I haven't had a proper relationship with a woman. I don't mind a friend asking me that once but it started annoying me once she'd done it a few times. She eventually got the point when I asked her how she knew she was straight when she hadn't either. She's a really sweet lass, it just took her a while to get it.

(*)shorthand term, my sexuality is more complicated than that but bisexual is easier to understand