Cutting in line: Is it ever OK?

Saw something at the grocery store Saturday that's been nagging at me ever since. One of those everyday scenarios where you can read anything you want to into the situation and come away from knowing only how you would react.

I'd just finished paying for my groceries and was swinging my cart toward the exit when I noticed two older Asian women with greeting cards in their hands, not far from a young guy who was next in line and unloading his cart onto the conveyor belt. One of them nodded in his direction and gestured toward the conveyor, asking if it was OK to go ahead of him.

He shook his head no and pointed to the line of three, maybe four, people behind him, all with carts at least half-full.

My gut reaction: What a jerk. What's the harm in letting someone with one or two items go first? Especially two women who, based on their appearance and body language, were first-generation immigrants with limited English. I imagined the gumption it might have taken for them to ask, only to be dismissed without a word, just a quick jerk of the thumb toward the back of the line.
 
The more I turned it over in my mind, the more I tried to see it from multiple perspectives.
 
Were they wrong to ask? 
Was he wrong to say no?
Is it fair to the people behind you, if you say yes?
Did race or ethnicity play into this?
Would he have said yes to a white woman? 
To an attractive young woman?

Maybe he was in a hurry. Then again, maybe not.

What about you?  Do you let people go ahead of you? Under what circumstances?

Photograph: www.thetalkingmirror.com