A couple of jobs ago, I worked somewhere with an excellent code review culture, and it began with a simple, written standard, very small, that everyone had agreed to. I now refuse to review code unless I am able to say "This code doesn't conform to the document you agreed to; it's not that I think this is bad code, it's that it doesn't meet the document that you agreed to." If there's no document to point at, no objective standard to meet or not meet, I'm not reviewing it because it's just not worth the tantrums and screaming from precious programmers.
There also need to be consequences for code that doesn't meet the document; basically, it's not ready to merge/commit until it does. There needs to be a way to allow code that violates the standard to be waived and permitted, with agreement from the developer and reviewer, with the waiver recorded so the developer feels listened to and the reviewer feels protected.
You're going to have to get buy-in for this from someone with power and authority.