Do something in a careless, slow, lazy way, and you're doing it lackadaisically. If you're rushing to get ready in the morning, you'll be frustrated when your sister is hogging the bathroom, lackadaisically brushing her teeth.
The adverb lackadaisically comes from an old expression, "lack-a-day," which expressed regret or sorrow — sort of like saying, "woe is me" or "alas." Lackadaisically was originally used to mean "in a sentimentally woebegone way," but at some point lax, "loose or languid," started to alter the way people used the word. Today if you act lackadaisically, you're halfhearted or even lethargic. If you study lackadaisically, you're unlikely to ace your vocabulary quiz.