If both item slots are empty, each unused action point gives you a +2 instead of +1 towards your Armor Class at the end of your turn, plus 1/12 of your unarmed skill.”— Fallout 2 (patched) In-game description
While it states that both item slots must be empty, that is not entirely accurate. It would be better to say that you cannot be holding a gun or melee weapon (anything that is visible in your character's hands). This perk will work if you are wielding unarmed-class weapons (such as brass knuckles, boxing gloves, power fist), grenades, rocks, or any non-weapon item.
HtH Evade shares the Vault Boy image with Artful Dodger.