(YouTube link)
Is there a law somewhere that says we all have to face the same direction in an elevator? Apparently so, since we all obey that law. This old clip from Candid Camera is funny because we all understand it. In real life, the behavior is a little more ambiguous, as seen in the elevators of the London Underground that have doors on both sides of the elevator. http://www.spring.org.uk/2008/08/elevator-psychology-and-london.php
I actually prefer to stand by the side (not back) wall and face into the center of the elevator. Also, I think it's safe to say that's pretty staged although it would be a fun experiment to try :)