oil and water don't mix

Proverb

 * 1) Black people and white people should not form relationships;.
 * 2)  Some people, things or characteristics do not go together.
 * 1)  Some people, things or characteristics do not go together.
 * 1)  Some people, things or characteristics do not go together.
 * 1)  Some people, things or characteristics do not go together.