What's in a phrase?

… apparently, for too many, a lot: About Last Night | The problem with “no problem”. (Hat tip, Dave Lull.)

Above all, though, I was struck by the furious resentment that came boiling into my Twitter feed as a result of my casual observation, as well as by the assumptions implicit in this resentment. It was, lest we forget, a one-sentence tweet devoid of context. Nevertheless, many respondents seem to have taken it for granted that I was portraying a real-life encounter between a haughty middle-aged man of means (i.e., me) and a poorly paid millennial convenience-store clerk (i.e., them). And while hundreds of people earnestly assured me, some pleasantly and others less so, that there is no definitional difference between “No problem” and “You’re welcome,” I soon lost count of the responses which made it crystal-clear that there is, at least for these particular respondents, a huge and purposeful difference.

I can't say I've ever heard someone reply to my "Thank you" with "No problem."  But it does seem odd. How does the an expression of thanks connect with the notion of a problem? And I'm no baby boomer. I'm older than that. I did find it amusing how some seemed to think that because you are old, you are also feeble. Some old guys are quite capable of kicking the shit out of people, even people younger than they are.