I was paying the receptionist after a massage, and when she handed me the receipt, I said "Thank you." She replied: "No problem."
Now, I don't even blink at "no problem" in other situations. I ask for a new fork and the waiter brings it; I say "thanks" and he says "no problem." I ask the mechanic, "Can I leave the car overnight?" and he says, "No problem." I’ve always assumed the complainers were objecting to this response, which seems completely normal (if casual) to me.
But these interactions were different from the one at the massage place. I asked the waiter or mechanic for something, got it, and thanked him. In those cases, “no problem” (as The Ridger notes) is no more rude, contentwise, than the time-honored “it was nothing” or “don’t mention it.”
In the transaction at the cash register, though, no service was requested or granted. My “thank you” for the receipt was just part of the minimum ritual – you hand me a receipt, I acknowledge it. In response, either a return “thank you” or “you're welcome” or even a cheery “mmm-hmm” would have been normal, but "no problem" sounded distinctly odd. It seemed to say "yes, I did you a service," when that wasn't the case.
So maybe the “no problem” problem is more subtle than I’d thought. For me, it seems, some “thank you”s can be answered with "no problem" and some can't. Is this true for (some of) the people who object to "no problem," or is theirs a blanket condemnation? And does the distinction exist in other languages that use the equivalent of "no problem, it was nothing" as a response to "thank you"?
Or have I just been thinking about this non-problem for too long?