Three points:
- first of all we all balls things up. i know i have. the only difference is that some are lucky enough to do it in a fashion where it is subtle and doesnt get noticed where as some unlucky sods do something not so subtle and get it printed in the press. No one can possibly tell you something (ie what were you thinking? you have learned a valuable lesson etc etc) that you havnt already told yourself. i know this from experience.
-2nd as an ex instructor the renewals/revalidations/club check types especially the cocky ones are ALWAYS the ones to really watch out for. like someone else said on here, the good ones dont need to talk about how good they are.
-3rd. although i am not in a position to say this for sure; i should think this should not be a career blocker for you. People who have been around in aviation long enough have all made mistakes and know it could have been them. so long as you werent downright negligent and being a real cowboy then they can put themselves in your shoes and identify with you. nothing better in an interview than an interviewer that knows precisely where you are coming from even if he doesnt want to admit it.