In the series, he is shown to be a party animal and falls asleep a lot. He is quite friendly toward others. He can also be a bit lazy at times. He will usually offer people to bungee jump from his armpit hair, such as Banana and Lady Primavera.
Armpit Willy is grayish-green and he never wears a shirt. However, he wears a pair of black tight shorts and a red toboggan. He has chest hair, and has long armpit hair.