Touch Me Not

This spell charges your body with protective energy. You gain a +2 bonus to your Armor Class. In addition, an opponent that touches or grapples you takes 9 (2d8) points of radiant damage. This spell is purely defensive. It does not make you armed, nor can you use it to make a touch attack, though it does deal damage on any enemy with whom you grapple.

An ally can touch you without taking damage. 

At Higher Levels. When you cast this spell as a 3rd level  spell, it grants a +3 bonus to AC and deals 3d8 damage. When you cast it as a 4th level spell, it grants a +4 bonus to your AC and deals 4d8 damage. And when it is cast as 5th level spell, it grants a +5 bonus to AC and deals 5d8 damage.