Underwear that you keep in the back of your drawer just in case but they are no longer part of your regular wardrobe. IE they are ugly and your partner doesn't like them.
Bob says to Billy, "Yo Billy, i bought us a six pack for the game"... Billy replies "SHUNDIES in your UNDIES" - with the accent on shundies and big ending on the undies!!
white boy: daaaaayum girl send me ur slundies ;) ;) ;)
best friend: lets show each other our slundies and check they're okay before you send them to anyone and I'll compliment you a bunch aw aw you're so hot