between you, me and the bedpost

between you, (and) me, and the bedpost

What is going to be or has been said should not be told to anyone else. This phrase is usually said along with information that needs to be kept secret. I overheard the boss talking to her secretary last night and—just between you, me, and the bedpost—she's giving the promotion to George after all. Between you and me and the bedpost, Stephanie is not as qualified for this job as she claims to be.
See also: and, bedpost

between you, me and the bedpost

or

between you, me and the gatepost

If you say that something you say is between you, me and the bedpost or between you, me and the gatepost, you mean that the person you are talking to should not tell anyone else what you have said. Between you, me and the bedpost, I'd say he was completely confused. Between you, me and the gatepost, he'd be better off without her. Note: People also sometimes use fencepost instead of bedpost. That's my opinion, between you, me and the fencepost.
See also: and, bedpost