The evening before Valentine's Day when you are supposed to take out your mistress. Whereas on Valentine's Day you take out your wife or girlfriend.
I told my wife I was going to play basketball with the guys on mistress night, but I really took Susan to dinner.
by Patrick Ransom February 13, 2010
In the old days, 'mistress of the night' or 'lady of the night' meant that a women was a suductress, harlet, or whore. It also is a statement that applies to certain pop culture madams, such as Elvira. "Unpleasant dreams..."
by Jennisis January 28, 2016