A man walks into a bar and asks the barman for a glass of water. The barman pulls out a gun and points it at the man. The man says ‘Thank you’ and walks out.

This puzzle has claims to be the best of the genre. It is simple in its statement, absolutely baffling and yet with a completely satisfying solution. Most people struggle very hard to solve this one yet they like the answer when they hear it or have the satisfaction of figuring it out.