Reading books, listen to music, playing piano, chat with friends...But actually I can't remember a moment when I really had nothing to do - that's what I understand is boredom
If I have time to be bored, I will sometimes go wreck a lot of cars online. I would have to be indestructible and a billionaire to be able to handle the amount of carnage that happens. The graphics are sure good nowadays.
When I'm bored, I like to pick up any book and just read or listen to music while writing down things. Youtube and facebook are also good distractions.