I was in McDonalds today (don't ask), and there was a single line in front of the one attended register. One of the staff opened a second register, but everyone happily stayed in one line. Here's the dialogue that followed:
McDonalds : "Please form a second line here"
Steve : "Why?"
McDonalds : "What?"
Steve : "Why should we form two queues, when one queue is more efficient?"
McDonalds : after 3 or 4 second pause, "Because I say to"
Can't argue with logic like that....