Watching guys masturbate has always been one of my biggest turn-ons, and I once had a boyfriend who would basically jerk off for me whenever, wherever, and however I asked. I often would even make videos of him stroking himself so that I could masturbate to them later, eventually I compiled about two dozen of my favorites into a 'special' DVD.
I had a roommate that semester and one day I 'accidentally' left my 'special' DVD in the player when I went out of town over the weekend. Sure enough, when I got back and restarted it, it was at a different 'chapter,' so I knew she had looked at it. I never mentioned it to her or to my boyfriend, but to this day I like to fantasize about her watching my boyfriend jerking himself off over and over, and in the back of mind I hope she made a copy and is fingering herself to his hottest jerk-off sessions right now.