What is another word for be as different as chalk and cheese?
Pronunciation: [biː az dˈɪfɹənt az t͡ʃˈɔːk and t͡ʃˈiːz] (IPA) 
The phrase "be as different as chalk and cheese" means to be totally dissimilar in nature or character. If you're looking for other ways to express this idea, you might say that two things are like night and day, apples and oranges, oil and water, or cats and dogs. Another possibility is the saying "poles apart," which suggests a vast distance between two things in terms of their attitudes or outlooks. Whether you're writing about contrasting personalities, disparate interests, or incompatible ideas, these alternative expressions can come in handy when you're trying to convey the idea that two things are diametrically opposed.
