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.
As a tutorial grade react developer (please return me to the backend where I am mediocre instead of bad), having more senior developers take the time to explain why my code was bad was really helpful.
Also I think I just kind of hate JavaScript. It always feels like everything is more complicated and booby trapped than it should be.