When you save your best pair of panties or undergear for that right fuck.
Usually knickers that are racy, c-thru, frilly or elevate the bulge or pussy with a low sexy cut.
I waited for him to leave the house and then told Mom.
My Mom clawed his eyes out and ripped his naughty knickers off and burnt them.
My Dad don't have naughty knickers anymore.
But my Mom still does :p