expression, noun
oil and water; incompatible things or people
Idiomatic expression describing two things or people that do not mix well, like oil and water. Often used in the pattern ～は水と油だ.
あの二人は水と油で、一緒に仕事をするのは難しい。
Those two are like oil and water; it's hard for them to work together.
His opinion and mine are completely incompatible.