Do something vapidly and you're acting without any energy, enthusiasm, or inspiration. If you vapidly tell your friends a story, they're bound to get bored before you finish.
This adverb connotes a certain dullness and emptiness — vapid was used in the 17th century to describe fizzy drinks gone flat and stale. It goes back to the Latin root vapidus, "(something) that has exhaled its vapor." This lack of flavor is reflected in vapidly. Smile vapidly at someone and your heart isn't in it. Recite your lines vapidly on stage and you may be replaced by your enthusiastic understudy.