None of these effect me any more because I was little, but still...
Have You Seen This Snail? - The animation of the heart metronome in the song bit used to scare me crapless when I was really little, so much so that I'd deliberately skip that episode on the Where's Gary DVD
Procrastination - The whole entire scene with the candle and the talking house, and just- eeh
All That Glitters - The same reason Larry22 mentioned
Wormy - The close-ups of the horsefly. Whenever this episode would air, the moment I saw the title card, I'd switch to Cartoon Network as fast as I could.
The Sponge Who Could Fly - The patchy segment at the end with the mariachi band and the the magnetic tape from the vhs flying out of the VCR and on to Patchy and him screaming and the camera panning up to the night sky and the french narrator telling you to get lost used to terrify me when I was little. This developed a very VERY shortlived fear of magnetic tape flying out of a player, only for it to be revived the first time I watched Atlantis Squarepantis. (once again, it was very shortlived)
Truth or Square - The hell demon version of painty in the live-action intro, and the scene with Patchy inside of the whale and the film burning up
Atlantis Squarepantis - The scene with the aliens, and the part where Patchy's Ultra Rare Frampton Comes Alive 8-track gets destroyed.
Walking Small - The part where SpongeBob suddenly grows an elephant trunk used to unnerve me
Squidward in Clarinetland - "I don't like your tone" and just the whole bird sequence in general
Planet of the Jellyfish - Do I even really have to explain this one? I legit had nightmares from this when I was little. I'm not kidding about that.
Can't think of anything else, so... yeah. lol
