Touch Me Not

This spell charges your body with protective energy. You gain a +2 to your Armor Class. In addition, an opponent that touches, grapples, or hits you with a melee attack immediately takes magical piercing damage equal to 2d4 + your spell casting modifier. It does not make you armed, nor can you use it to make a spell touch attack, though it does deal damage to any enemy with whom you grapple once per round at the start of their turn in addition to any damage the grappled enemy ends up doing to itself by hitting you.
An ally can touch you without taking damage.
At Higher Levels. When you cast this spell using a spell slot of 3rd level or higher, the damage increases by 1d4 for every slot level above 2nd.