The SpongeBob episode you're thinking of is probably 'The Camping Episode' from Season 3, where SpongeBob and Patrick pretend to be sick to skip work and go jellyfishing. It's one of those classic episodes where their antics spiral out of control—first with the whole 'fake sick' routine, then the chaotic camping trip that follows.
What makes it memorable is how absurdly committed they are to the bit, especially SpongeBob's over-the-top 'illness' acting. The way Mr. Krabs falls for it hook, line, and sinker is pure gold. If you're craving that mix of childish mischief and surreal humor, this is the episode to revisit. It’s a perfect snapshot of why early SpongeBob still holds up.