Personally I have two tones I take in a code review comment: the "Should ... ?" form for when I want to raise awareness but otherwise leave it up to the other p

Personally I have two tones I take in a code review comment: the "Should ... ?" form for when I want to raise awareness but otherwise leave it up to the other person, and the "I recommend ..." form for when I think there's a real issue. Especially in the latter case, I'll back it up with a real-world scenario of how it could cause a problem; either a bug, difficulty reading the code by future maintainers, or making it more likely to introduce a bug when the code gets refactored later. Finally, back-linking to documented standards if necessary to avoid the appearance of a me-against-you type of thing.