I close the stall door even if I'm standing. Of course, that isn't always a safeguard as demonstrated in
this thread.
I prefer my privacy whilst engaged in this particular function, maybe I'm a bit kooky this way, but I prefer avoiding circumstances like what happened when shesus and I first started dating. I went to her parents' house for dinner and went to grab a soda. In order to do this, I had to go down to the basement, past one of their bathrooms and what did I see but her father with pants around ankles, bathroom door wide open and whizzing away gleefully. So yeah, I always close the door, even in a public restroom.