Your favorite NON-recurring Seinfeld character...

[Brian]

Oooh, damn. I was just watching Seinfeld and am dismayed to say that The Bubble Boy would have to be disqualified under the strict "1 episode only" qualifications, as he appears briefly in "The Pilot: Part 2":

(Donald and his parents from 'The Bubble boy'. We see his arm coming off the bubble, between his parents. He doesn't have the TV remote anymore. His parents are laughing)

DONALD: This is a piece of crap!

MOTHER: Donald, you used to like him.

DONALD: What a sellout! Give me that remote!

MEL: No, Donald.

(he grabs the remote from his father's hand and the three of them start to fight)