No problem is not ungracious. It functions in exactly the same manner as you’re welcome. What is ungracious is getting pissy when someone responds to thank you with no problem.
Icarus, I dunno what you’re on about. This is a thread about things you wanted to say and did. I have a lot to say on the subject of etiquette and I’m gonna say it. Totally on topic. 
I get the feeling that the people who hate ‘no problem’ are the ones who think that retail salespeople are not really actual people, they’re just servants who are there to do the customers bidding, no matter how unreasonable the customer acts.
Just because someone makes minimum wage doesn’t mean you can treat them however you want. No, not even because you are ‘paying their salary’. The store can get by just fine without your patronage, I assure you. And if you are given friendly, prompt service with a smile but you still leave in a snit (or worse, make a scene) because that darn cashier didn’t follow the exact script you would prefer, then really you’re the one with an etiquette problem.
I tend to use “no problem” if I’ve done someone a small favour and they thank me for it - maybe they’ve dropped something and I’ve helped them pick it up or given them directions, whatever.
In business terms I would always say “you’re welcome” if being thanked for whatever service I had supplied.
Unless they were being sarcastic in which case “fuck you asshole” is more appropriate. (:
No, turn the damn phone off. Unless you’re a ER Doc on call, in which case wtf are you doing watching a movie in a theatre?
On to “No problem” I am a bit older than most posters and I have no problem (heh) saying it or hearing it.
Two, movie related:
From best friend—he and his wife were seeing Titanic, cut to ship going down. From seat in back a gaggle of girls exclame “It"s SINKING”. Wife whips around and asks “WHAT movie do you have tickets for?”
Former projectionest—at movie with then wife, dealing with screaming baby in back of theatre, the ex-wife loudly demands “Would you give that kid some tit?”
As was said in the movie Clue; “Too late!”
Actually, I’ve been a retail salesperson. And I dislike “no problem”, though I never indicate it when someone says it to me.
As far as “no problem”, I can’t imagine any scenario in which it’s some kind of calculated response, let alone an intended offense.
In almost any case, it’s a scripted rhetorical response to a scripted rhetorical pleasantry.
The only time I’d consider offense would be based on vocal tone.
I’ve long ago learned to have a very high bar for taking offense at written Internet things given that a lack of emoticon leaves one with no usual real life cues (tone, facial expression) to moderate meaning.
Big rolly eyes here. Huge rolly eyes.
The first rule of the Internet is “don’t extrapolate emotional meaning outside of real life visual cues”. The Internet is at least twenty years for most people. How can this most basic of lessons have escaped you?
Befuddled. I guess some people want to find offense.