Best Brief Appearances?

I was watching the Sixth Sense again the other day, and I'm just always blown away by Donnie Wahlberg's performance and how well he sets the scene for that movie despite only being in it for like two minutes. Another one that always struck me was the guy who played Elmo Blatch in the Shawshank Redemption. Just a great, creepy performance that really underlined the reveal that Andy was actually innocent. It got me to thinking, what are some other brief appearances like this that you felt were really impactful? I'm not talking about *cameos*. Doesn't have to be a famous actor. I'm talking about scenes where an actor really nailed the performance in a very brief amount of screen time. Thanks!