While trying to avoid getting dirty on his way to Mrs. Puff's Boating School, SpongeBob is squirted ketchup on by a group of teenagers and an old man attempting to squirt it on his hot dog.
"Little Yellow Book"
Squidward has SpongeBob deliver a bag of ketchup to the dumpster in the back of the Krusty Krab, which Patrick is inside. Patrick then takes the ketchup out and remarks that it would be a good combination with an old diaper he found.
Ketchup, along with mustard, appears in Battle for Bikini Bottom at a condiment bar in the Krusty Krab. When SpongeBob is granted access to the restaurant, he is able to destroy various property of it, including the two condiments.
Ketchup appears in SpongeBob Moves In! as a cooking material made in the Krusty Krab. It requires two tomatoes to be made. It takes four seconds to make, gives 1 happiness when collected, and gives 8 coins when used.
Patrick likes to put ketchup on diapers, as seen in "Little Yellow Book."