How in the world can those be comfortable? It isn't really necessary to tell you mom what you wear under your clothes. Just make sure you keep them out of the regular laundry.....don't want her accusing you dad of something he didn't do.
Tell her it's the latest fashion of men's underwear and they're called banana hammocks.
For whatever reason you're wearing them I doubt that it's for comfort. I'd find a more plausible excuse than that before I dropped them into the dirty washing.
Something teens often overlook is that their mother's are pretty smart. She'll know, Brandon!