What's your favorite proof accessible to a general audience? What math statement with proof do you  find most beautiful and   elegant, where such is  accessible to a general audience, meaning you could state, prove, and explain it to a general audience in roughly $5 \pm\epsilon$  minutes. 
Let's define 'general audience' as approximately  an average adult with education and experience comparable to someone holding a bachelor's degree in any non science major (e.g. history) from an average  North American university.

I would explain the Pigeon Hole principle, or one of its many guises.
In fact, I remember explaining the PHP to a non math student while playing bridge.
I told him that one gets at least $4$ cards of some suit- which is really the PHP.
You can come up with many other interesting "real life" examples, and it's fun.
