Naughty nightwear (Fallout 3)

 is a set of leopard skin pajamas found during the unmarked quest Grady's Package in Fallout 3 and at Mick and Ralph's in Fallout: New Vegas.

The outfit can be repaired using various "pre-War" and merc outfits including pre-War hats.

Unmarked quest: Grady's Package
A humorous side quest (actually a sub-plot to the Nuka-Cola Challenge) involving the naughty nightwear can be found in Marigold Metro Station, which is near Grayditch.

Bugs

 * The naughty nightwear's world model is bugged; when dropped, it looks identical to the sexy sleepwear. The all-nighter nightwear, however, displays an accurate world model, leopard-skin and all.
 * When you are accosted by Lug-Nut, if you drop the nightwear before talking to him, he still thinks you have it. Furthermore, if you "give" it to him, he'll spawn his own 100% condition copy before running off. Killing him will net you two copies of the nightwear.
 * When handing in the naughty nightwear to Ronald in Girdershade, if you managed to exploit the Lug-Nut "drop" bug previously, you cannot hand in the quest with two instances of the naughty nightwear on you. Simply drop one and then talk to Ronald to complete the quest.
 * It will sometimes disappear from the player's inventory only to never be found again.

Fallout: New Vegas
This item is purchased from Mick at Mick and Ralph's in Freeside. It can be found in his "special" stock. After you pass a speech check (30) and Mick opens the "special" stock, you can reach the Naughty Nightwear through the bars of the shop and steal it if you don't want to pay for it.

You can also find it in the ultra-luxe penthouse area, in a crate in the room with a couple of heck's guards (assumed to be his suite while he is staying on the strip).