A terrible manager is a free course in everything you’ll refuse to do to people later.

Bad treatment teaches precisely and for free. Working under someone who takes credit, changes the plan without telling you, or only speaks up to criticize gives you a very exact record of what it feels like from underneath. Most people never get that detail about their own behavior until they cause it. You are being handed a list while it still costs you nothing to read.

Write down three specific things the person does that land badly, in the plainest words you can. Keep the note. The day you are the one running something, that page will be more useful than any advice about leadership.