Mr. Burns: Ketchup. Catsup. Ketchup. Catsup. K- K- Oh, I’m in way over my head.
Store Guy 1: He’s, uh, talking to the ketchup now. Burns is sure acting nutty.
Store Guy 2: Maybe going broke and losing his plant destroyed his brain. Could you come along with us, sir?
Mr. Burns: Are you here to solve my ketchup problem?
Store Guy 1: Yes. That’s right.
Mr. Burns: Wh-Where are you taking me? What’s happening?
Chief Wiggum: Relax. You’ve gone off your nut so we’re stuffing you into an old folks’ home. Those, uh, store guys signed the commitment papers.
– The Old Man and the Lisa

The Simpsons | Season 8 - Episode 21

There are numerous articles about the difference between Ketchup and Catsup on the internet. Two things that I learned after reading these articles are:

• There is no real difference between Ketchup and Catsup
• Everyone references Mr. Burns Ketchup vs. Catsup confusion in their writing because the scene is hilarious

Personally, I was raised eating Heinz Ketchup and I’ll die eating Heinz Ketchup so my allegiance is clear. I like to think of Catsup as “Non-Heinz brand tomato, sugar, onion, salt, cinnamon based sauce” and that helps me keep things straight. I guess that wouldn’t look very attractive on a bottle label though. Also, Catsup is apparently not sold at my local grocery store.

Incidentally, Smithers actually wanted Catsup based on his grocery list:

So I’m left to conclude the Catsup is preferred by people like him…you know, Personal Assistants.

Cromulence: (Ketchup NOT Catsup) 10 Adorable Little Ragamuffins out of 10

No Fuss, No Muss Ketchup vs. Catsup From: The Old Man and the Lisa (The Simpsons Season 8 – Episode 21)