One of my fave times is sitting ny a window riding a dildo. The dildo is not visible, I slide up and down, discreetly at first but the pleasure builds and my need to climax. Occasionally someone will pass by but I can't stop. I wonder if my movement & the expressions on my face give me away.
I actually do this myself sometimes. I'm staying at a motel on the 1st floor so I open my blinds just a little and masturbate, using my dildo to fuck myself. I always get so excited at just the thought of someone seeing me!