Your conversation should read:
Person 1: Coca-cola and Pepsi have identical ingredients.
Person 2: No they don't.
Person 1: Well, based upon my experiments and observations I conclude that they do.
Person 2: Your experiments were rubbish, because the drinks have different ingredients. Besides, the ingredients are right on the bottle, and they're clearly not the same.
Person 1: The labels are wrong.
Person 2: What makes you think they're wrong?
Person 1: Because Pepsi and Coca-Cola have the same ingredients.
Person 2: No, they don't.
Person 1: Then why does every experiment we've performed and every observation we've made indicate that they do?
Person 2: They don't. And I have evidence to prove that the ingredients aren't the same, but you don't have have any at all.
Person 1: I think they do, and my evidence is based on personal observation and experimentation. While yours is based on nothing but other people's data, which you have no way of verifying
Person 2: *rants angrily then gives up*