Please forgive my cynicism. I spend a lot of time in Great Debates and I don’t agree with the majority of the folks in there, so I’m used to innuendo in responses to me. I’m sorry if I seemed defensive or snarky.
To answer your question, anytime someone butchers or dumbs down the English language, it gets under my skin. Bad grammar also sets my teeth on edge.
How is “back in the day” any different than “sets my teeth on edge”? Both are phrases that, given just the words as they are constructed, don’t necessarily mean anything. However, they are both common phrases that are used by people to express a certain meaning, one which most listeners (or readers) understand.