I think it would be useful to have a reject reason "This should be a comment".
Whenever I see (minor) edits to code or some edit that challenges the opinion in the original post I select "other" and write "This should be a comment".
My reasoning behind is to reject the edit but to give the editor a hint what he should have done.
Recent example: http://stackoverflow.com/suggested-edits/317430
if aline in m.keys():
if aline in m
A comment would have been a better option compared to a straight edit.