Just the fantasy of wearing someone a suit, that makes you appear as someone else. This goes a bit further in stories by TheSamMoose, where people wear suits, that transform them into separate body parts, but the general idea stays the same. A really nice addition, of course, is when a character decides to wear something under the skinsuit. The difference between this here and Human Mask is that a skinsuit makes your entire body appear to be normal.
Sara's Mannequin Suit by VolatileDesire
Quite a long story from a sticky-site archive I found. The story begins with a bet between Gawin and Sarah and with Sara winning, Gawin has to wear the fetish cat costume he had originally planned for Sara. Sara’s Mannequin Suit by VolatileDesire Chapter 1 - A Clever Bet The room was filled with a soft light shadowing the faces of the couple facing each other across the dining room table. Two glasses half full of wine rested next to two piles of discarded playing cards. The woman idly flipped through the fan of cards in her hand while rubbing her opponent’s leg with her dark nylon encased toes. ...