The social law that if you hear a reference to an arcane or forgotten word, idea, or person, you will encounter that word, idea, or person again in the near future.
"Yesterday, I learned the word 'soporific,' and then it was used on the Daily Show tonight! It's Darby's Law!"
"Oh my god. There was a major Darby's Law today. I hadn't heard about Bill Nye the Science Guy in years until we talked about him in English class. Then he was in my science textbook the next period."
An internet law similar to Godwin's Law, which originated in a myspace political group when people couldn't stop derailing threads. It postulates: "As an online discussion grows longer, the probability of weight or body image being discussed approaches one."
I was just trying to make a point about the difficulties women would face in the military, and all of a sudden someone starts bitching about how larger women aren't accepted in society. Darby's Law strikes again.