Ever have a hard time explaining to the un-cycled why you ride a bike? It always amazes me how such an efficient and healthy activity could be questioned, looked down upon, or even ridiculed. Here's a handy visual that covers a lot.
"Puts a big fat smile on your face" ranks number one with me. Depending on your level of fanaticism, explanations for lycra shorts and leg shaving may take a little more work on your part.