(of people) to say the opposite of what someone else has said, or (of one fact or statement) to be so different from another fact or statement that one of them must be wrong:
Examples:
If you're both going to lie, at least stick to the same story and don't contradict each other!
(of people) to state the opposite of what someone has said, or (of one fact or statement) to be so different from another fact or statement that one of them must be wrong: