> Something that drives me nuts is someone writing on a code review "you may want to consider using the X data struct here" and meaning "I will not merge this code until you use X"

The former language is appropriate when there is a specific problem to be solved and X seems to be a good solution. This language doesn't rule out other approaches that also solve the problem. (It should probably be accompanied by a good description of the problem.)

Saying the latter would be fairly rude since it implies that you think an ultimatum was required to get compliance. I'd instead phrase it as "X data struct should be used here." It is still clear about the correct way of doing things and carries less baggage.