Even though in the episode Traffic Troubles Johnny cannot sing, he has been able to sing in previous episodes.
Johnny: Hey! Where are the chicks?
Old Lady: Right over here, big boy.
The episode Traffic Troubles marks the second appearance of the Sensitive Male. He hasn't appeared on the show since the first season.
Carl makes a brief cameo appearance in the episode My Funny Looking Friend, when Johnny was opening auditions for funny looking friends. He has been re-drawn to fit in with the animation style used in the first season of the show.