bjoc
Besides Jill, of course. Used to indicate that something is intended to be kept secret, except from your BFF Jill, of course. This is applicable regardless of whether or not said BFF's name is incidentally Jill, as long as both parties in the conversation understand who "Jill" is.
O.M.G. did you hear that Ryan showed Sophie how scissoring works using a fingering demonstration??? But don't tell anyone, bjoc!