Spongebob Squarepants - The Original Fry Cook's Hair.
In the episode "The Original Fry Cook," a frycook named Jim comes back to pay a visit to the Krusty Krab. Jim was the original frycook before Spongebob. A big deal is made about his returning to the store, enough in fact to make Spongebob jealous. At one point, Jim and Mr. Krabs walk by the wall with several of Spongebob's Employee of the Month pictures posted side by side and directly on top of each other.
When Jim points out, "This is new," Krab retorts, "Don't worry, we still have your's up." Krabs then proceeds to knock down all of Spongebob's pictures and underneath them is a huge picture of Jim located directly below the title of "Best Employee Ever."
The slip is that in this picture, Jim has no hair. Later on in the episode, we see a flashback of Jim and why he quit the Krusty Krab; only in the flashback when he leaves (angrily) he has a full-head of hair. Would he leave angrily only to return to have his picture taken some time later?