The first time.
Regardless of the situation, if it be starting a new job or taking a new special someone out on a date, experiencing something for the first time is unpredictable. You can approach the situation with boatloads of false bravado, but deep down inside there is always some level of nervous tension that can throw you off your game.
Sure, all of your jokes and cracks of wise might have worked with your previous beau or boss, but this is unfamiliar territory and you don’t know how things will play out. As much as you want to draw on previous experience to boost your confidence, the uncertainty will keep you off balance.