Careful with this one. In my experience, you aren't fooling anyone when you ask someone a question to which you yourself know the answer. It can quickly come off as condescending.
One helpful practice that we have is that we make a distinction between blocking and non-blocking comments. Nonblocking comments are desired changes, but aren't required by the submitter to fix (formatting, code simplification, naming, etc). This steers people in the right direction without preventing them from getting work done. Blocking changes are critical things which must be resolved before the code gets merged (security risks, performance concerns, complexity concerns).
And of course, every comment should be followed with a suggestion for how to resolve it (even if it's meeting in person). "This is bad" obviously doesn't fly.