Dan Quayle is the infamous "potato" politician.

English isn't a particularly easy language, on a relative basis, at least for those who don't study it academically at the post-grad level. "An" vs "A" is one of the last errors I'd ever fault someone for, because it's poorly defined and tends to have precious little impact on the actual meaning of the overall sentence.

Is it a marginally annoying error when I "know" what's correct in my head and I'm listening to someone else make the error? For sure. Would I ever point it out to someone on their second, third, or fourth language? Not a chance, because it's largely an irrelevancy and also damnably difficult to explain efficiently as a "rule".