That’s fine; you’re welcome; I’d be glad to help. This conventional reply expressing acquiescence and other positive feelings originated in America in the mid-twentieth century. It also has taken hold in numerous parts of the non-English-speaking world; the author has heard it in France, Austria, Yugoslavia, and Singapore from individuals who otherwise knew almost no English (other than “okay”). Others report having heard it in Russia, where it is often used ironically, Kenya, and China. In Australia, however, it alternates with no worries (probably from the 1930s British locution, not to worry). The journal American Speech recorded “no problem” in 1963 as an equivalent of no sweat. The OED’s citations include Martin Amis’s Rachel Papers (1973): “He . . . gave it back to me, saying ‘No problem’ again through his nose.” It has quickly become as ubiquitous and as divorced from the words’ original meaning (i.e., “there is no difficulty”) as have a nice day and take care. Indeed, Pico Iyer pointed out that today “ ‘No problem’ . . . in every language means that your problems are just beginning” (Time, July 2, 1990).

A person who agonizes unduly, anticipating failure or disaster or other misfortune. This slangy term, also spelled worrywart, dates from about 1930. For example, “‘So who’s alarmed?’ I asked. . . . ‘You were, Mr. Worrywart. You saw the Health truck outside and what did you think? Sickness’” (James Patterson, London Bridges, 2004). See also nervous Nellie.