I used to be a gentleman. Then I dated a feminist.
Seriously though, I find that generally, girls these days are quite undeserving of any "chivalrous" action. Like many of you have said, lots of them are so block-headed they hunt for that "sensitive man" and end up with complete arseholes, and you can see it a million miles off, wondering how they can't. Then they turn to you, the supporting friend, when it all goes wrong and you try not to say "I told you so".
My current girlfriend loves to be treated like a princess, but the problem is that gentleman side of my has disappeared, and a cynic has been left in his place. When I meet new people in particular, I can't help but feel that they're idiotic hypocrites when it comes to their pursuit of a perfect man.
This is a complicated issue. In short, no, I don't advocate chivalry, because in my experience it's largely unrewarded. I believe in equality, real equality. Yes, that means I believe in splitting the bill etc. Why should it be a man's responsibility? Sometimes there are exceptional circumstances, but on the whole, I don't see why that should be the man's "duty". That kind of mentality just encourages women to keep believing each of them is a special princess worthy of royal treatment by all throughout their lives. This, obviously, is ridiculous, and if anything, the previous generation's level of chivalry is to blame, instilling in their daughters the belief that all men should behave as they have.
I frequently feel judged by my girlfriend through the filter of her dad's morals, and constantly reminded of the things that a boyfriend "should" do - much of which often makes me roll my eyes in consternation and laugh at how ridiculous it is at the same time. Maybe it's just me, but I feel that chivalry is a negative thing, because it leads to a generation of pampered, preening girls who believe it is their God given right to demand any damned thing they want and get it, right then and there, with a bow on top, BECAUSE I WANT IT.
Back to the issue at hand though: we simply don't know all the facts of the situation. Yes, I think he was wrong to say "stupid stupid stupid", BUT I do understand that he probably felt quite embarrassed in front of the cashier - as a previous poster said, why go up to the cashier to buy stuff if you don't have the money on you? You look like a fucking fool. Obviously he himself wasn't expecting to pay for it as he said "oh are you going to pay for it?"
As another person pointed out, there's the possibility that they had arranged for her to pay for something now and he pay for something later. We just don't know. Maybe they'd been arguing. Nothing is ever as clean-cut as it looks.