Used Napkin is an inaminate object which only appears in the episode I Had an Accident. It is a napkin which has presumeably
SpongeBob holding it.
been used from its name. SpongeBob personified it after going insane from being isolated in his house, like as an example saying "That's enough with the name calling Used Napkin!". Used Napkin is one of three "friends" SpongeBob made after deciding to live inside. The others being Chip and Penny.