Užupis is a neighbourhood in Vilnius, which has declared it's independence from the rest of Lithuanian! I'm not sure if this really counts as a country, hence I've added it to my 'Honourables' list.
However there is a written constitution for Užupis, which more than you could say for the United Kingdom! There are 41 points, and here are some of them..
4. Every one has the right to make mistakes
12. A dog has the right to be a dog
20. No one has the right to violence
27. Everyone shall remember their name
37. Everyone has the right to have no rights