A real friend argues with the mean things you say about yourself. Loudly.

Most people let self-criticism slide past because it sounds like modesty, and staying quiet feels polite. A good friend hears it as inaccurate information and corrects it the way they would correct any other wrong fact. That is not flattery. It is somebody refusing to let you be the only one describing you, particularly on the days your description is not reliable.

When a friend runs themselves down this week, do not laugh along with it. Name one specific thing that contradicts what they said, and be concrete rather than sweet. Then listen to how you talk about yourself around them, because they are paying closer attention than you think.