Related to #4, but subtly different; Proof by Observation.
I can think of a few people who have passed many of the other proofs, but failed the Observation test. This can occur in person, but also in online social interaction. I essentially watch how a person interacts with other people, especially when they are in a position of power relative to the other people.
I guess it could also be called the “Jerk Test.” Does this person behave decently with others?
I’ve witnessed very intelligent and otherwise trustworthy individuals break down in the comments section on social media. They become defensive, rude, or insult the intelligence or belief system of anyone who dares to challenge the original post.
“Two things define you. Your patience when you have nothing, and your attitude when you have everything.”