By a show of hands, folks, let's see how many of you are offended by this....
You go out somewhere, anywhere really, and someone helps you. A waiter, bank teller, the lady at the drycleaner's, your friendly neighborhood grocery store. You, being the polite person that you are, give your helper a hearty "thank you." And what do you get in return? "No problem!"
Why in the world do people say that? It drives me nuts. By reassuring me that what I've asked for is not a problem, you're really telling me that it actually it is a problem, but you don't want me to think that it is, so you tell me it's not. Makes me crazy.
Why not just say "you're welcome" or "my pleasure" or "any time?" This holds true whether you've helped a customer, a co-worker at the office, or a total stranger. Don't diminish your act of helpfulness by declaring it's no problem. Just say "you're welcome," and maybe flash a smile.
You'll feel better, and your "thanker" will feel better, and the world will be a little bit better because of it.