I thought about my answer, since many mechanics I don’t like can have good implementations, or at the very least are a sort of lesser of two evils kind of thing.
What I can’t stand are tactical or RPG games with realtime or turn based combat option toggles. I play many games with one or the other and enjoy them, but when I play a game with both that can be toggled in options I always feel like neither setting feels perfectly right. The balance is always off no matter what. Understandable with game devs having to double the amount of work for creating combat and tuning items and it ends up feeling a little soggy every time.



Respeccing. It shouldn’t be infinitely free, but I like games that allow you to pay (usually increasing amounts) to respec.
Related to this, in older games without this it was common practice to save up your skillpoints and just sit on them until you’d gotten a little further into the game and hopefully had a better idea how to spend them. What was massively frustrating in older games were when leveling up forced you to immediately spend the points instead of sitting on them.