The next person has to be ready to reach for the slice. I don't care if someone is intending to get a slice. The slice is being grabbed or the box is closed. It's like holding the door open. If it shuts before you're in reaching distance, your timing wasnt correct. It's never rude to shut the box, it always courtesy. This is serious pizza business, and right now our world runs on pizza time. Guess what? It's pizza time.