What makes a guy turn to his back to the door and stand there and look at you from a distance?

There were two cops that were walking out of the cafe with food. And as one of them were leaving, he stands at the door and turns around so his back is on the door and he just stares from a distance for a bit before he walks out. I even did a double take to see if he was looking and he just kept looking at me until he pushed it open and left. So I’m wondering what this behavior was about?

What makes a guy turn to his back to the door and stand there and look at you from a distance?
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