Ironguard

At-will, swift, 3 Mana, concentration; you modify your own body, such that, when interacting with metal objects, it is as if your body is made of water. If a metal weapon is thrust into you, it just schlorps in and back out, causing no damage. All other material types are unaffected.

If you are holding a metal object or wearing metal armor, it is affected, but consider that most weapons have non-metallic hilts and metal armor should pretty much always have layers of cloth underneath it. But yes, if you insist on wearing a chainmail bikini, it will schlorp right off (and good riddance to the pinching).

Rules lawyer info:

• To determine what a "metal" is, consult the periodic table. Metals in an amorphous state still count as metals.
• A better guideline is to consider your body a hologram with respect to metal. If you insert two metal plates stuck together into your body, then separate them (like a stage magician), they don't pull your halves apart, they just schlorp.