Warning: this post is mainly Menshevik Sophism, defending the Regime against change. However, this part is good:
"With humans, the right way to deal with behavior you don’t like is to talk about it, another time—or at least, with some kind of context switch. That prevents the natural conflict response in which the human, nagged, digs in and persists in the behavior as a point of honor, or even just a way of getting attention."
Sadly, the mature way to deal with conflict is to assume the other person isn't going to be able to be mature about it.
Though if you think about it, this makes sense: if they were a fully mature and realized, they would have asked first instead of causing a problem, or used one of many other equivalent pre-emptive measures. Recognizing you might be causing an issue is not rocket surgery, it's the simple act of being considerate. When a conflict arises, you can safely assume one or both of you is being a brat.
This means you need to give them time to get out of brat mode and return to mature adult, then speak to them about the behaviour.
To repeat: don't assume it was them in brat mode. Could well have been you. Certainly, you will have the urge to immediately snap at them about it, like a brat. Then you're guaranteed to both descend into brat mode.
As a proper nihilist I must acknowledge that, you know, maybe you enjoy being a brat? Is that what you prefer? I've never seen it in the wild, however. In the wild, I see regret.
There's a bunch of little tricks like this for dealing with conflict efficaciously and efficiently. Luckily, like this one, they can largely be derived using babby's first empathy. "If I'm being a brat, how will I react if someone addresses my brattiness immediately? Why do I react that way? Oh duh, I guess I shouldn't myself do that, either." Though, refresher: test your conclusions with an open, curious, non-arrogant mind. Babby's first empathy only works reliably when individuals are identical, i.e. it is not reliable.
P.S. This 'be positive' thing is really hard.
P.P.S. Just because you don't like a behaviour doesn't mean you're entitled to have your partner stop doing it. Nihilism: you're only entitled to something if you literally have a contract (a 'title'), signed by the relevant parties, saying you're entitled to it. E.g. maybe they messily eat peanuts on the couch, and you somewhat don't like that, but they really really enjoy letting loose sometimes. Getting outraged that they won't stop is narcissistic manipulation, not setting healthy boundaries. Or: if you really dislike the peanut thing so much, you should have noticed before you got married, not tried to use relationship health or respect or whatever to manipulate them into stopping. By getting married before talking about it, you're implying you were okay with it, and you don't get to change your mind - even if you do change your mind, that's your problem, not theirs.
(This is one reason I'm in favour of sex before marriage. Otherwise you get surprise conflicts you can't possibly know of beforehand. That said, this does require effective birth control. Further, sex should be considered a promise to marry, because women will feel attached like a fiance regardless of whether it's socially considered that or not.)
To repeat: much of this relies heavily on the respective affect intensities. If you really really hate it and they haven't even thought about it before, then okay, you still should have talked about it before marriage, but mistakes happen. Don't cancel the marriage because of an oversight about peanuts of all things. Once you are properly [neighbours] then Yeshua is not wrong about forgiveness. Forgive them for the peanuts. Have them forgive you for being anal. Re-negotiate post-forgiveness.
P.P.P.S. It does get complicated pretty quickly; ref: see above. It's not just one or two tricks here and there. Normally you would rely on the culture to guide you so you don't have to re-derive all this from first principles, but unfortunately you can't rely on the local culture. Indeed, the local culture says to get divorced immediately if not sooner, so...