One thing that I think gets lost a little in our age of blameless retros, blameless post-mortems, and blameless code reviews is that sometimes it just boils down to: your code is bad.
This can be hard to stomach, but it is part of the learning and growing process. You're not going to become a better developer if you can't, from time to time, come to grips with the fact that you just made some gross mistakes in that code you just wrote.
Honestly, if you aren't looking back at code you wrote 6 months ago and grimacing, that's an indication that you aren't improving.
I'm not suggesting you roast your colleague in that next code review, but don't don't shy away from pointing out embarrassing mistakes, even if you have 3 years experience and you're reviewing Ms. 20-years-experience-senior-staff-engineer.
On the other hand, if you're on the receiving end of one of these reviews: don't get defensive, don't lash out, don't cry. You're privileged to get this feedback and you should use it as motivation to knock it out of the park on your next PR.
It's a cliche, but the best developers are the ones who are always learning and improving. None of us have it all figured out, even if some of us are good at pretending like we do.