Hi,
a) Don't quit. The "on top of the world" feelings you've had so far are nothing compared to the ones you will have in the future!
b) Change instructor.
c) If the instructor who said the examiner would laugh at you is young, point out that he'll never get an airline job with an attitude like that!
d) While flying with someone different, concentrate on doing right the things that he pointed out you were doing wrong!
e) Everyone goes through a phases where things go wrong and you seem unable to fly properly. With me, this phase was in the hours leading up to my GFT. Don't let it get you down.