No we haven't "all done it" and what you describe doesn't amount to gross misconduct either. Any decent employee representative or employment lawyer would take your "secret black naughty book" management approach to the cleaners.
It ended with either deliberate wrongdoing or gross negligence by GP which was so serious that it fundamentally undermined the relationship of trust and confidence between him and his employer; for this (gross misconduct) he was fired. Whether previous personal performance and achievement etc...