I take the Fifth
I take/plead the Fifth (Amendment)(American humorous)
something that you say in order to tell someone you are not going to answer a questionSee a fifth wheel
Usage notes: The Fifth Amendment is the part of American law that says someone does not have to answer questions about themselves in a law court.(sometimes + on ) 'So who do you like best, Jenny or Kim?' 'Sorry, I take the Fifth on that.'