Average Joe is the third part of the 25th episode of season 2 in Dexter's Laboratory. In this episode, Dexter starts to live an average life after his intelligence test results came back as "average."
Dexter's class runs an intelligence test. His result: average. The boy genius is shocked to see this, and then decides to leave his laboratory behind, and just live as an average joe - even if the only clothes he has other than were ones he hadn't wore since he was a baby! He then befriends an average kid, Jimmy Smith.
The baby clothes Dexter wore re-appeared in the season 3 episode "If Memory Serves".