On a occasion when I am waiting for a female friend (just a friend, nothing more) to come over, I'll masturbate in my room in hopes that they'll show up a little early and catch me.

I think that stems from a time I had a female roommate and she cracked my door open and asked me a couple questions one day while I was masturbating, her view was blocked by a wall, so she didn't know what I was doing (I asked her later). I also used to masturbate while talking on the phone with girls, which is similar to exhibitionism.