In the episode where Rocko accidentally wins the tickets for the monster truck show or the wrestling event (I can't remember which) and Heffer and Filbert argue over who Rocko should bring with him, watch the part when Rocko wakes up the morning of the show (when Heffer has hancuffed himself to Rocko.) When Rocko wakes up, he has his undershirt on. Then, when he is walking down the stairs, he has his normal purple triangle shirt on. Then, when he walks to the threshold of his door, he has his undershirt on again!