Patrick's underwear is a character who only appears in the episode "The Gift of Gum."
Patrick's underwear is an old pair of underwear that is colored white and light blue. It also has pink gum on it from Gummy. Disturbingly, it's sentient and is capable of speech.
Role in episode
Patrick's underwear is seen after it crawls out from Gummy. It crawls onto SpongeBob's face and tells him in a raspy voice, "You're not Patrick." SpongeBob screams in terror when he hears this and Patrick's underwear crawls away.