final fling
One last particularly fun time before a dramatic change occurs in one's life, such as a marriage or the birth of a child. Come on, you need a final fling before your wedding—let's go to Vegas for the weekend!
final fling
Fig. the last act or period of enjoyment before a change in one's circumstances or lifestyle. You might as well have a final fling before the baby's born. Mary's going out with her girlfriends for a final fling. She's getting married next week.