I have corrective tourette's. At least that's what Allison calls my subconscious utterances.
Let me explain. We had a professor last semester who always said the "width" (correctly) and the "heighth" (incorrectly). I can't tell you how many times I turned to see what Allison was laughing at, only to discover that she was laughing at me. I was always surprised when she pointed out that I'd just quietly muttered a "t" sound after the professor in question said "heighth."
It's not deliberate or malicious. I don't know why I do it, when I have no intention of ever saying anything to the professor. I suppose it's one (weird) way to counter my own cognitive dissonance.
And then there's my entirely obnoxious habit of correcting other people's grammar. I've mostly learned to temper it and bite my lip when "farther" and "further" or "continually" and "continuously" are misused. But I'll admit that it makes me a little bit itchy each time I remain silent.