Where's the Ketchup?
As mentioned earlier, the toppings are just as important as the Hot Dog itself. If you look at the required toppings for a Chicago Dog, you will notice that Ketchup is not listed among them. Ketchup is an ingredient frowned upon by Hot Dog aficionados. Although ketchup remains one of the most popular condiments on Hot Dogs, "properly made" Hot Dogs, like the Chicago Style, usually lack the condiment.
Those who consider themselves Hot Dog connoisseurs are often vehemently opposed to eating (or even witnessing) Hot Dogs with ketchup; they think the flavor of ketchup overpowers and destroys the taste of the Hot Dog instead of complementing it. Nowhere is this difference in opinion more apparent than in Chicago.
The inclusion of ketchup on a Chicago Style Hot Dog is a controversial issue. Most adult Chicagoans will shun ketchup. Chicago Hot Dog stands will not, as a rule, put ketchup on a Chicago Dog. Some stands will provide ketchup although you are responsible for defacing your Dog.
"You know what makes me really sick to my stomach? It's watching you stuff your face with those Hot Dogs! Nobody - I mean nobody puts ketchup on a Hot Dog!". - This is a famous line from the movie Sudden Impact starring Clint Eastwood.
The National Hot Dog & Sausage Council, in its recommendations for proper Hot Dog Etiquette capitulate only slightly to the public's general regard for ketchup, saying "Don't use ketchup on your hot dog after the age of 18.".