In this case, the joke is that someone with a dairy allergy could somehow buy and eat ice-cream without knowing it contained dairy. It's just a completely ridi

In this case, the joke is that someone with a dairy allergy could somehow buy and eat ice-cream without knowing it contained dairy. It's just a completely ridiculous thing to check. Like warning that the boiled peanuts contain peanuts, or that a pencil sharpener should not have fingers inserted into it.