Everybody...get in line.

I was at a store yesterday, waiting in line along with five other people, to pay for a purchase. A man came into the store with a bag, walked right past everyone waiting in line and asked the clerk, who was serving someone at the time, if he had to wait in the line if he wanted to return something. When the clerk answered yes, he reacted angrily and stomped his way to a spot at the end of the line and fumed.
Somebody...please...help me understand.
I mean, I get that he didn't want to wait in line. I'm very impatient and waiting in line is so overwhelmingly unproductive on so many levels that few things in life aggravate me more. The fact that there's nothing you can do about it doesn't comfort me. In fact, it just frustrates me even more.

Nothing you can do about it, Clark. Might as well just stand here and wait.

What?!? I'm an American. I can do anything I want!

Nope, not now.

Why? Why can't I do anything about it?

There is no answer. It's just one of those things.

That's stupid. I don't accept that. There's an answer for everything.

Hush, now. And stand still until it's your turn to move forward another 18 inches.

AAUUGHH!!! I'll kill you and everybody else here!!

So yeah, I understand that.
What I don't understand is the mindset at work here. What was he thinking? Did he really think that the clerk was going to make people who got there before him to spend their money, wait while she gave him money back? Did he really think he didn't have to accept the stupid reality that everybody else does? I'm standing in line, he has to stand in line. Who does he think he is?
Some of you humans, man. I just don't know.