Armpit Willy has a strange reaction to peanut butter which causes his armpit hair to grow to extreme lengths. When this happens, his armpit hair gets a mind of its own and grabs things, such as Banana in "The Chronicles of Cutesachusetts".
He sometimes lets people bungee jump from his pit hair.
He is good at playing the guitar.
There is a possibility that he models for Calvin Clam underpants, as an image that resembled him modeling in underwear briefly appeared in "Underpants-Palooza".
In "Mall Ya Later", his full name was revealed to be Willard Pittsworth III.
His surfer dude voice is an impression of Otto Mann, the school bus driver from The Simpsons.