Looking at all the comments, I thought that "button pushers" deserved another post!
First off, go here. It has good explanations not only for pedestrian and elevator button pushers, but also for honking in traffic jams, cable TV channel surfing, refrigerator door reopening, email box refreshing and hitting the snooze bar. All in all makes for a very interesting read. Thanks to whoever (Anonymous) left it in the comments section.
Some additional thoughts on the previous post - I firmly believe that crosswalk buttons are completely misleading. You have no control whatsoever over what the sign will do, and that any perception that you do have control is a complete placebo effect. I've never seen anyone press the button and shorten the interval for the light to change. People keep pressing these dummy buttons, thinking they have some modicum of control over traffic and their immediate path in life. But instead what they have is an illusion of control. The decision about when the light will change has already been made, independent of them and their button-pushing desire to move forward. For elevators however, there is no delusion of giving control. The only control that it offers is the ability to choose what level you want to go to. Beyond that there is no promise. So I guess, we can attribute this purely to impatience. Not that the earlier one cannot be attributed to impatience, but that does have an element of delusional control to it (which is the more overbearing reason).
As I sign off, I must admit, I am sometimes guilty of these too (more often wondering if I should do it again and having someone preempt the second pushing, than pushing repeatedly myself) ... and I do agree that it does not irritate as much as someone behind you honking at red lights!!!