Eventually I've told him "if your comment does not affect performance or business logic, I'm ignoring it". He finally got the message. The fact that he accepted this tells me that deep down he knew his comments were just bike shedding.
Then, going through their code, they make excuses about their code not meeting the same standards they demand.
As the other responder recommends, a style guide is ideal, you can even create an unofficial one and point to it when conflicting style requests are made
Yes!! Exactly. When it comes to my PRs, he once made this snarky comment about him having high expectations in terms of code quality. When it comes to his PRs, he does the things he tells me not to do. In fact, I once sent him a "dis u?" with a link to his own code, as a response to something he told me I shouldn't do. To his credit he didn't make excuses, he responded "I could've done better there, agreed".
In general he's not bad, but his nitpicking is bad. I don't really understand what's going on in his mind that drives this behavior, it's weird.
For example, most people would agree you should use exhaustive checks when possible(matching in rust, records in typescript, etc.). But how do you enforce that? Ban other types of control flow? But even if you find a good balanced way to enforce it, you won't always want to enforce it. There's plenty of good use cases where you explicitly don't want a check to be exhaustive. At which point now you gotta make sure there's an escape mechanism to whatever crackhead check you've setup. Better to just leave a comment with a link to your style guide explaining why this is done. Many experienced developers that are new to rust or typescript simply never think of things like this, so it's worthwhile to document it.