Naughty nightwear (Fallout 3)

 is a set of leopard skin pajamas found during the quest, Grady's Package, in Fallout 3.

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.

In Fallout: New Vegas
Purchased from Mick at Mick and Ralph's in Freeside, in his "special" stock.

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.