Tooth Fractures
One of the most annoying things that people do with their oral piercings (usually when they first get them) is incessant "clicking" and running the bars and beads along their teeth. This increases your risk of being slapped by people near you, as well as having the potential to damage your teeth permanently.
This type of constant minor impact can cause microfractures in your teeth (sort of like the spider-webbing effect you get in poorly maintained gel coats on fiberglass boats and cars). These leave the nerve of the tooth more exposed to temperature changes (which is of course very painful). In addition, even though cursory examination of the tooth shows no cavities, small particles can get into these fractures leading to even more pain.
It is important that you try and stay conscious of your habits. Don't let jewelry clicking become one of yours!