come off it
US /kʌm ɔf ɪt/
UK /kʌm ɔf ɪt/

1.
used to tell someone that you do not believe what they are saying, or that you disagree with it
:
•
Oh, come off it, you don't really believe that, do you?
•
Come off it, you know that's not true.
used to tell someone that you do not believe what they are saying, or that you disagree with it