Google publishes its guide for reviewing other engineers’ code. It advises reviewers to make comments “about the code and never… about the developer.” It gives a bad example: “Why did you use threads here when there’s obviously no benefit to be gained from concurrency?” The guide suggests marking small points with “Nit:” so the author knows they are minor.
The guide also asks for praise: “If you see things you like in the CL, comment on those too!” A CL is a change to the code. The reason, it says, is that “people learn from reinforcement of what they are doing well and not just what they could do better.”