Plastic Underwear is the twenty-eighth Butterfinger commercial featuring The Simpsons that first aired on December 31, 1999.
Lisa bites into her Butterfinger, awakening a sleeping Grampa. When he attempts to go back to sleep, the biting noise happens again, though this time it's not Lisa but Grampa's plastic underwear. Once Grampa is back sleeping Lisa once again bites her Butterfinger.
(Originally, Grandpa was mentioning that it was his osteoporosis, but he was overdubbed in this version)
No Teasing • The Butterfinger Group • The Bully • The Shrink • The Shock • Butterfinger Ice Cream Bars • Butterfinger on a Stick • The Pacifier • The Last Butterfinger • Bart's Karate Lesson • Good vs. Evil • I'll Be Your Best Friend • Maggie's Party • Bart's Homework • Beach - Homer With Crabs • Bart's Locker • I've Been Robbed • Crime of the Century • The Dog Biscuit • The Raid • Maggie's Party • Hit a Homer • Philosophy • Carnival • Aliens • Smell Your Breath • A to Z • Itchy & Scratchy's 500 Easy Pieces • Plastic Underwear • Butterfingeritis • Bart's Nightmare • Homer Holer • No Teasing • Itchy & Scrathy: Butterfinger Test • Dinner Butterfinger