It may sound odd to the uninitiated (and weird if you’ve read Divergent), but the one thing you do not want your character to have when they fight is piercings. Why? Because piercings are often put in nerve sensitive places: the ear lobes, the eyebrow, the nose, the lips, or simply embedded in the skin.
Combat is revolves around causing a damage to the opponent as quickly as possible. Ripping out someone’s piercings means that they will be put on the defensive, meaning that your character can move to the offensive by distracting their opponent with blood and pain (it’s difficult to fight if your eyebrow is leaking blood and clouding your vision or into your mouth). Pain in one region of the body, will distract the mind from pain in another, so while the opponent thrown back by the shock of “Oh god, you just ripped out my piercing!”, your character can be spending that time hitting them in the groin or the throat, or grabbing them and slamming their head/temple into a wall/table. Honor is a nice sentiment, but it has no place here: the highest priority in any combat situation is survival. Always take the advantage when it lands in your corner.
Studs are smaller and more difficult to grip, rings and any larger pieces are simply an excellent distraction piece.
Military Tip: For the most part, the Military outlaws piercings for men. It allows studs for women if they are in a non-combat position, however, it’s a bad idea. The only setting I’ve ever seen really get away from the piercing problem in a legitimate way is Warhammer 40k and their Space Marines. However, the Space Marines piercings are bolted into their skull. So, you know, good luck getting those out.
Protip: You usually don’t haul someone around by their piercings, they come out too easily and besides, that’s what hair is for.