email safe word
In an email thread, a word (usually irrelevant and strange in the context of the email thread) agreed to by the participating parties to change the subject or end the thread when the inappropriateness of the thread has reached its limit. This is so that someone on the email thread can let everyone else know that they feel like continuing the thread would only get too personal and cause shame.

Similar to a safe word in BDSM.
Bob: Notice her status says engaged as well…I wonder if this dude is her fiancé…or if that is why she has been abstinent?
Sue: I'm not even sure what to say but LOL about her "other pussy." She's a class act, right there. I just hope she wasn't friends with her co-workers.
Mary: That is exactly the reason I don't have a Facebook acct.
Jill: OMG…that was hilarious!!! Mary…..I don’t think we’d need to know about your escapades.
Bob: No, love caves are private.
Jill: I bet you are about ready for a visit to the love cave, aren't you, Bob??
Sue: BANANA! I said BANANA! Stop, dammit, stop! For the love of God, BAAAAANAAAANAAA!
Jill: Huh?
Sue: Banana is our email safe word. In order to prevent us from too much TMI, we need to put an end to this thread.