Being into history isn’t a red flag, but when it translates to ‘The Roman Empire was a perfect society with no issues or flaws’, that’s a Yeesh
Collecting a large number of alcoholic beverage containers may suggest a person's frequent or excessive alcohol consumption, which can be a red flag for alcohol-related problems.
Excessive gambling can be a sign of addictive tendencies, indicating that the person may struggle with self-regulation and impulse control.