A fork of Rural Dictionary
If one believes there is likely a mutual interest between themself and another individual, that other individual is either already in some form of a relationship with another individual or will soon be.
"I thought we were clicking, but then I saw her boyfriend."
"Rule 11, eh? Good luck next time."
Any person that one thinks is interested in them, is not.
"Hmmm, I think she likes me. Oh, Rule 10..."