If you hear something you disagree with, you are not in a position to voice your disagreement (peer pressure, etc.), but make at least some symbolic disagreement, for example paint a dot on the top of your paper.
Interesting idea; I might do that some day if I find myself in the ‘right’ (i.e. wrong) situation.
If it's worth saying, but not worth its own post, even in Discussion, it goes here.