Ned's Declassified School Survival Guide - Potty Mouth Janitor
In the episode titled "Rumours", where they try to make the school jump in the air by flushing every toilet at the same time, near the end where Sweeny & Gordy are trying to escape, listen carefully. Almost straight after Gordy says "Come on man!" or something like that, you can hear Gordy whisper "Oh S***"! I couldn't belive it at first so I rewound it and it is definately there. Before you say "He's just saying shoot!", please watch the episode, it's easy to say that if you haven't heard it.