Interesting, so "passive-agressive" is already built-in. Meaning even commenting in a very innocuous style "I'm not sure if this is correct according to the style guide..." would prevent a merge.

I personally try to encourage both communication and responsibility. So I comment on pretty much everything I don't understand/like/agree with (i.e. over-communication, that's really the only way to ensure adequate communication because by over-communicating according to your standards you're more likely hitting the other person's communication standards, which are necessarily different from your own and fundamentally unknowable), but at the same time I encourage the other person to decide which comments they want to respond to (either by arguing or by changing the code), hence showing I trust them and encouraging their personal responsibility.