Mine is that the useState hook is an actual plague on the entire React ecosystem. Regardless of your opinions of React, if you wanna use something then use it right.
I disagree when it comes to standardized single-letter variable names. They're invaluable when writing dense code for games or other math-heavy applications and you learn to recognize them very quickly.
So i for index in loops (and j, k for nested loops, but you're almost always doing something wrong if you need them); x, y, z for position and h, w for size; r, g, b, a for color data, etc - you'll immediately know what the variable is for at a glance even though it's a single character.
Another benefit is that having related variables be the same character width keeps code visually aligned, which helps with readability.