To unlock this Achievment you have to slot armor in the head, chest, shoulders, waist, hands, legs and feet. I unlocked this while playing for Aldmeri Dominion.
In Skywatch, Auridon, head to Aegis of Auri-el where you can find armor to steal for your head, chest, shoulders, hands, legs and feet.
Waist took me some time to find as it's in random boxes, Wardrobes or urns. I just searched in everything possible till it came up.
Once you have all 7 pieces of armor, equip them all and perform a crime. Pay the bounty and the achievement will unlock!