I suspect that “being good at languages” and linguistic pedantry must be fairly firmly linked, because most of the people I know who enjoy studying languages other than their own also seem to find misuse of their own language annoying. I’m a big fan of Lynne Truss’s Eats, Shoots and Leaves: the zero tolerance approach to punctuation and belong to the Facebook group “The Panda Says No” and there are a number of things in both written and spoken English that make me cringe.
My current least favourite is the tendency of people in the circles in which I move to see hoi polloi as a synonym for “the elite”!! As in “there I was, sitting at the main table with the hoi polloi”. Yeah. Right. Unfortunately, it never seems to be said in circumstances where I can reasonably explain to the speaker (and hearers) that hoi polloi is Greek for “the citizens” so the kindest translation is “the people” and it is more usually taken to mean “the rabble” or “the great unwashed”.
While I am prepared to agree with The Chicago Manual of Style and Meriam Webster’s dictionary that it probably does need a “the” in front of it in English, despite the technical tautology, I cringe and shudder whenever I hear a usage that is so clearly wrong in meaning. Why do people have to use words they clearly don’t understand????
And on a related note, the Sydney Morning Herald has a section called Column 8, in which readers write short pieces about odd things that catch their attention and often bemoan ecentric uses of language. One of their current topics is the use of “an” rather than “a” in front of words beginning with “h” – you will need to scroll down a little. I have been known to say “an hotel” occasionally and also “an historic even”, but never “an happy new year” nor “an hat”. My understanding is that “an” goes with words borrowed from French where the “h” is not pronounced. Je pense que je suis un peu pédant. 
I’d love to hear readers’ pet linguistic peeves.
