I have a doppleganger in San Francisco. His name is Doug, he's Canadian, and he goes to Walgreens and buys rubber duckies, then sits around grinning going "I have ducks."
There's something fucking weird about being around a person who acts just like you, no matter how cool he is (and Doug is cool). At some point I realized I was looking at him sitting there giggling about his ducks and wondering if that's how I look to my friends. (Short answer: yes.)