Personal hot-button:

I go off when presented with historical revisionism, even minor stuff with good intentions.

Like people arguing that the modern definition of a word has always been and the old definition as false.

Or my favorites (sarcasm) that I see all the time is the expanded proverbs treated as the original, claiming that people are misquoting when they're using the actual provably original quote. Yes, the expanded ones are better... but they're not the original!

For example I commonly hear people "correct" the proverb "blood is thicker than water" to claim that it's a shortening of "The blood of the covenant is thicker than the water of the womb." I get pissed every time I hear that.