Only ask for the Ketchup when you are wearing full protective armor. (Ha ha!)

Maybe he means there is no way to serve you ketchup. Because in 'traditional' french food, ketchup is not a French product. For example, we have mustard (de Dijon) for French fries... Ketchup is considered as a foreign product (American product made in Germany... oh my gosh). Can you understand now it could be an insult to ask a French chef for ketchup...

With a large arrow pointing to you saying ' I'm a foreigner who doesn't appreciate the fine culture of French cuisine. Have pity on me.'

It would be sacrilege! A downright insult! :D