I think the key is that if you ask a question, you should be willing to accept "no" as the answer. Sometimes the answer is "not now" or "no", and perhaps adding a TODO or a comment explaining why not.

Particularly well-explained code shouldn't raise any questions.

I suppose so. Most often I don't harp on stylistic choices that don't affect the integrity of programs. I might encourage another coder to lint their code, for example, but I won't specifically single any of those out. I just won't waste time asking questions if I find ten places the program could error out on.

I agree. My preferred phrasing uses “we” (we are working on this code together) instead of “you” (you are working on this code and I am telling you off) and is usually a sort of polite suggestion with concrete justification. For example:

Another thread could have modified ‘x’ between when we test the condition and when we take the lock, so we should test that ‘x’ is ‘NULL’ if ‘y’ is true here, and if not, sleep and retry.