Why are people antagonistic?

Neil and I were out at Jade Tree for Monday Night Chinese(tm) yesterday. While we were having a nice little dinner by ourselves, a woman ended up arguing with Sophie, who owns the restaurant. The woman was stating "This is wrong. Last time I ordered the tofu wasn't fried..." while Sophie was telling the woman "then last time they either lightly fried or incorrectly made your order."

The woman arguing had that antagonistic hauty "I'm better than you" feel to her.

I just can't understand it.

Neil and I, when we do have a problem, we don't make a scene. We politely tell the waiter there's a problem. It almost always gets straightened out... and if not, we just don't go to that restaurant again. I guess it also helps that we're relatively big tippers. Unless they auto-tip (I really hate that) we will leave 20% for basic service and if it's great 30% or more. But, when they auto-tip, we leave only the amount they've decided should be their portion, which is normally 15%.

Mel