I know this is a common complaint, but people writing common expressions wrong, because they've only ever heard them and don't realize they're using a homophone instead of the right word.
Reign in -> Rein in. You're pulling the reins on something to control it, like you do with a horse
Tow the line -> Toe the line, you put your feet behind the line that has been drawn by whatever applicable authority
Intensive purposes -> Intents and purposes. Self explanatory but the mistake also limits the meaning, instead of all the cases, it's only the intensive ones.
Picked/Peaked/Peeked my interest -> Piqued my interest. Piqued means excite, it excites your interest, it doesn't select your interest, make your interest take a look, or reach its maximum point.
Baited breath -> Bated breath. Bate means restrain, you're holding your breath as you wait or expect a thing. Your interest isn't being drawn by bait.
Wet your appetite -> Whet your appetite. Your appetite is sharpened, like with a whetting stone, it's not moistened.
Many more, but those exist in the front of my mind and I see them everywhere, even here, and I SEETHE EVERYTIEM.
Tow the line is one that really gets me. Given the themes of freedom of expression and virtue signaling and people conforming to The Cathedral and similar things we often discuss here, seeing it over and over just fucking infuriates me.
And also:
I could care less -> Fuck you and everyone who has ever known you