what makes a good day?

Most days I ask my son how his day was at school.  I get the usual, fine, ok, nothing exciting happened, boring.  Yesterday he said he had a great day.

I was thinking he must have done a really cool lesson in science, or maybe played something fun in PE.  So, I asked him what was so great about the day.

He's such a funny guy.  He pulls down the top of his pants to reveal his underwear and says, "I was wearing green underwear!"

Not sure how the color of underwear makes your day better, but hey, I'm all for improving my day too!