Detention is a common form of discipline in schools. It can occur during lunch, after school and or on a Saturday. Most of the time detentions are so boring you may feel like you are going crazy. However you can have fun during detention, provided you don't get caught.
Meditate. Learn how to meditate on a single word or mantra or learn the mindfulness meditation that completely clears your head of all thought. The time will float by, and you'll leave the room relaxed and centered.
Put your mind somewhere else. Compose a scenario in you head, your own screenplay and watch it play out in your imagination. If you're allowed to write in dentention, jot your thoughts on paper. You might have a great film inside you.
Turn your imagination into an iPod. You probably can't listen to the device in detention, so "play" music in your head. Think of your favorite songs and imagine they are playing. Hear the music and lyrics. You can go through entire CD's during one detention period.
Read a book. Draw a picture. Do your homework. That last one might not be fun, but it will free up your time to do things you enjoy when you get home.