Apples and oranges are often used to describe two things that are completely different and cannot be compared. There are other synonyms for this phrase that you can use to spice up your language. Polar opposites is a suitable synonym that can be used to refer to items that are very different from each other. Another great one is chalk and cheese, which is often used to describe items or people that don't have anything in common. Fire and ice can also be used to describe things that are unrelated. You can get creative and use these synonyms in your writing instead of the typical "apples and oranges" to make your work stand out.