Dirt

The Boss told me today that he "had some dirt" on me that would make me blush.
WHAT THE HECK WAS HE TALKING ABOUT???
I'm not a member of any secret club, I don't participate in any obscure sexual rituals, and I can't really think of any skeletons that are locked away in my emotional closet.
What possible piece of embarrassing evidence could he possibly have come across?
I'm confused. He probably just did that to irritate me.