@Myredhulk, "Calm down" puts pressure on the listener to actively negate their emotions, whereas "let's take a step back" is more neutral and less confrontational. It's like the difference between trying to push water through a drain vs just pulling the plug.
Try “you must be on your period, because you’re too emotional right now, sweetheart. You need to calm your tits, love.”
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Don't know why, but telling, and being told, "let's take a step back" actually works decently, even though it's functionally the same as "calm down".