I tried once but was unsuccessful (I think). I was on a trip and staying at a motel, two female friends were staying a few doors down. I left the chades closed but open by the door just wide enough that someone at the door would be able to see me on the bed from the waist down (this would feasibly allow me to claim innocence as I wouldn't be able to see them directly). We were planning to meet up and they were going to swing by the room. My plan was for them to "catch" me going at it when they came to know at the door. Unfortunately they called me up a bit early and suggested meeting at the car. It's possible they walked past the room and saw me but I honestly doubt it.
On a related note, when I was a freshman in college I was enjoying some alone time, cock in hand, while my roommate was at football practice when I heard a knock at the door. I called out something like "hello" or "who is it?" and heard my friend Laura on the other side. I barely had time to pull the blancket over me before she let herself in. I think she wanted to go to dinner or something and I had a hard time trying to think of a way to get her to leave so I could get dressed - I was nude from the waist down. She even sat on the bed while we talked! I finally persuaded her to leave though I can't remember how. I would have loved to show her what I had been busy with but she really wasn't the kind of girl who would take that well. Still, it was a pretty exciting situation.