a sexual activity where a girl or a woman takes off her knicker to masturbate, to copulate etc.
It can also be used for a couple when the man strips off the girl's panties and gets off with her with any sort of sexual game from masturbation to penetration
"The two of them did plenty of panty action before they tied the knot ".
What happen when a guy shows his boxers to a girl, either intentionality or unintentionally. This could be because of sagging, a hole in his jeans, or the popular way, pulling up a piece from the top of his pants and yelling "Panty Action!"
Allie saw Nathan's boxers through a hole and screamed Panty Action!