cumderwear is the nickname for old, dirty underwear. the name was established due to the fact that many people liked to jack off into old pairs, as it was easy to clean up the cum. but cumderewear is not just a word that describes using underwear for masturbation. it can refer to a ripped pair, a worn out pair, or a pair that was stained by a peeing/pooping accident.
whenever i'm looking at porn on the computer, i put on a pair of old cumderwear and jack away.
i had to throw away that old pair of cumderwear after the hole got too big.