An esoteric doctrine explaining the bizarre reasons chicks hate each other and are no longer friends. It can be applied uniformly to all women who borrow any type of clothing, accessories, electronics, etc., and don't return said item, leading to a downward spiral in the strength of the friendship. Occasionally, the jeans incident doctrine may lead to the creation of mortal enemies.
Ex #1: "Yo man, you hear Anna isn't talking to Katie anymore?"
"Really, what happened?"
"I think Katie borrowed her favorite scrunchie without asking, classic jeans incident doctrine at work"
Ex #2: "You can't invite her boss man, Jamie is going to be there, Shelly and Jamie hate each other now"
"what,... did Jamie borrow her jeans and not return them or something?"
"yeah, the proverbial jeans incident doctrine rears its ugly head again"