If there is one thing that Seto Kaiba can’t live without, it’s coffee. He pretty much lives and breaths the stuff. And he usually takes it black, or just about as bitter as humanly possible. It just isn’t pure coffee to him anymore if something is added to it.
Ryou, on the other hand, is not a big fan of coffee and it has to be sweetened. He cannot drink coffee black, nor does he want to try it again. In the hot beverages department, he is much more a tea drinker than a coffee drinker. He drinks it to calm his nerves while coffee just makes it worse.
Kaiba does drink tea on occassion, but he mostly prefers coffee. He doesn’t like feeling relaxed too often and the tea usually has a calming effect, which makes him nervous not being totally aware of his surroundings.
The only beverage they really have in common would be wine at parties. Otherwise, they don’t agree too often about beverages.