Nick Cave. I recall it was at a music festival many years ago. He'd set up a table for signing autographs and no-one was going up to him. He was quite engaging and approachable.
Ben Stiller. I had taken the ferry across Lake Champlain to the NY side to visit a friend. We decided to stop in a coffee shop for coffee and a pastry. He was sitting at a table drinking coffee and reading something. When we walked by, he said hello to both of us and invited us to sit down at the table with him. We chatted with him for about 20 minutes before he told us he had to leave. Very nice man.