Doug's Shock Therapy / Doug Is Hamburger Boy - S3-E11
Plot hole: Doug recalls previous years (in a flashback, where he was next to Skeeter at the window of the Honker Burger as they looked outside) of seeing the Hamburger Boy when Mr. Dink is confessing that he *was* Hamburger Boy. However, Doug has only been living in Bluffington for one year - this was his first summer there.
The Seven Crystal Balls: Part 1 - S3-E3
Plot hole: Two clown performers finish their act and the curtain closes. Tintin and Haddock then talk for a bit about who will be performing before the musician, but within the span of merely just a few seconds, the next act is suddenly on stage and ready to perform. No way could the clowns have left the stage and the next act have been set up within that short of a time span. (00:04:45)