A: Mustard. (It's good for a hot dog.)
Because dogs can't whistle. (X-post from r/dadjokes)
Your dog, because it'll stop barking once you let it in.
Mustard in a rollerskate
Cause ketchup accidentally broke the condiment.
Frank
Elderly me: I made my kids steak instead of hot dogs. Him: *gasps* You monster.
Because he had fever!