The GURPS 4th edition rulebook says this on the skill "Holdout" (concealing objects on your person): "A Las Vegas show girl in costume (-5 penalty to skill) would have trouble hiding even a dagger. Of course, the show girl might escape search entirely (unless the guards were bored) because 'She obviously couldn't hide anything in that outfit!' Full nudity is -7 to skill."
Hunter: The Vigil advises this as a method for hunters to gather necessary information on your enemies, and with the mechanics of such rolls in the game, you can say anything you want and the dice will still go in your favor.
Paranoia has a skill dedicated to this, Chutzpah. The example used to explain the skill is standing before a judge to be sentenced for murdering your parents — and pleading for clemency because you're an orphan.
Ork Commandos in Warhammer 40k are fairly skilled at being stealthy, but their greatest strength is the fact that no one is expecting Orks to be sneaky.
Cards Against Humanity thrives on this trope. Think Apples To Apples, except dirtier… much, much dirtier. Cards such as "Pac-Man uncontrollably guzzling cum" and "50,000 volts straight through the nipples" are particular standouts.
This is so much a part the Exalted mindset it's used as a basic mechanic, called stunting. Describing particularly epic things gets you bonus dice, with more dice awarded for more outrageous actions. The in game explanation for this is that the spiders who maintain causality never get breaks and watching stunts is the closest thing they have to entertainment. Out of game, it helps make games livelier and more enjoyable for the players.
While one could say that Infernum does this with its mere existence — who ever heard of a game devoted to playing as a soul-eating member of the Legions of Hell? — but it has more concrete examples, too. For example, one chain of powers is called "Chain of the Crawling Flesh". Its final power? You can shed your skin and then it will fight alongside you as a living entity in its own right.
Both Warhammer and Warhammer40000 live and breathe this trope. However, special mention has to go to Harpies and Daemonettes, whose official models (especially in previous editions) were both topless and anatomically correct.