Our personal zone is that space surrounding us that makes us feel uncomfortable and on guard when intruded upon by someone we don't trust, usually a stranger. For many of us that zone is dynamic depending on the situation. It's funny how we'll crowd close enough into an elevator car so that we're actually touching and we're okay with that because everyone's personal space is compressed. Then five people get off on one floor. Now everyone else in the car spreads out and they're essentially equidistant from each other. A couple more people get out and the process repeats itself.
So there's a couple things you can do if you want to kind of freak someone out. If the elevator is full try to stand so that you trap someone in a corner. As the car empties, don't move. If the elevator is sparsely occupied when you get on then stand right next to one of the people already there. They'll either squirm out from behind you or just be very uncomfortable.
But be careful not to make them too uncomfortable...um...you know...not that I'm speaking from experience. I'm just sayin'.