People hide their character in speeches and leak it in parking lots.

Prepared moments are performances, and everyone performs reasonably well when they know they are being watched. Character turns up in the unrehearsed places: how someone talks to a waiter, what they do with a shopping trolley, how they behave when the interaction has no audience and no consequence. Those are the moments nobody thought to manage.

Watch the small unguarded scenes rather than the polished ones. Notice how a person treats somebody who cannot do anything for them. Then check your own parking lots too, because that is where your character is leaking for anyone paying attention.