Speaking as an US citizen...
It doesn't upset me to see people disrespect the flag if they're doing on purpose. That's free speech, and while I can disagree with their sentiment, and think they're assholes, my disagreement is likely with their grander message, than with some silly cheap flag that they paid for, just to wreck.
What upsets me is people who think they are respecting the flag, but have no fucking idea what that means.
If some religious twat is stomping on the US flag and burning it -- well, they're doing it wrong. Yeah, the stomping was disrespectful, but then you burned it, asshole. That's what you-re -supposed- to do if the flag becomes tainted. Way to go, you accidentally honored the flag. Go you. If in your country it is a massive sign of disrespect to fix me a grilled cheese sandwich, and then you come over here and fix me a grilled cheese sandwich? I won't be insulted. I'll be like, "fuck yeah, grilled cheese," and I'll om-nom that fucker right up.
There are lots of people, though, who -think- they're honoring the flag, when really they're also doing it all kinds of wrong. There are lots and lots of very specific rules about how to display the flag -- illumination, orientation, time of day, state of weather, the condition of the flag itself -- and there are instructions on what to do if you slip up on any of those (namely: burn it). Most people don't know about as much about those rules, as they do about the US Bill of Rights, which is to say, 'dick.' I see tattered, darkened, dirty, wet and otherwise dishonored flags all over the place, and where you'll find them most, is in the ironically hyper-patriotic bible belt (ironic because they're doing it wrong, and ironic because of their duelling allegiances, but that's another rant for another time). Bring up the fact that they're dissing on the flag, and get into the argument of your life, which brings me to my ultimate point.
I'm not especially patriotic, by the way. This country is full of problems (although most of them stem from misapplication/misunderstanding/simple fucking rejection of constitutional law), and certainly isn't intrinsically 'better' than any other. My problem isn't so much with the symbol or how it's treated; the flag isn't that important to me.
I just fucking hate stupid people.