For the true voyeur at heart.
I get extremely turned on watching men when they do not expect someone to be watching them. Where I live I go to the bookstore, and head straight to the restrooms. I head to the stall in the middle (where you have the urinals on one side and another stall on the other side). Then I look at the tiles behind me, that line the restroom walls, and watch men through the thin vertical gap of the stall wall do their business (the best restrooms I found out to do it in are the ones with good lighting and preferably a dark tile) thankfully the one in the bookstore has black tiles so it is really clear.
Every once in a while I find men masturbating or just doing the weirdest of things. It is a huge turn on. Oh yeah, when your in the middle stall make sure the stall next to you is a handicap one, or you won't be able to see anything, with the handicap one you can get a full view.