Make them having human qualities. Like if someone likes coffee and you tell them it sucks, that person will literally stop at nothing chewing your head off with paragraphs upon paragraphs of essay why it's good for you and how it is actually good and you just have sht taste.
Not that their whole personality is just coffee, mind you. It can link into something more like this person likes bitter coffee, so naturally he'll also like food with strong tastes, or maybe coffee is even affecting how they act because of caffeine that they can't stay still in one place, or they can't start their day without the usual cup.