Junior is a major character in the first act of the short "Reason and Emotion."
He starts off from the beginning as a toddler, pushing a flower pot off a windowsill and clapping, as he only has Emotion in his head. Since Reason is not yet born, Emotion is free to dictate Junior's life, as shown when he has Junior pull a sleeping cat's tail and go downstairs. The results are getting hurt, and then Reason is born, and the battle starts.
When Junior grows up, restless Emotion causes him to look at a pretty girl, but Reason forbids him to bother her, and says to maintain proper respect for womanhood. Really insecure, Emotion knocks Reason out with his club and drives Junior to him, and has him ask, "Hi, babe. Goin' my way?" (Actually, Emotion says it.) The therefore-offended lady slaps Junior in the face, proving that not listening to Reason can get one in trouble.
He is never shown again after this.