So if one is approached by an F/O in a pub, it's time to start dieting?
I learn lots of useful stuff on here.
Pilot conduct is presumably overseen by the employer. Professional bodies are more common in occupations where people work for themselves, such as doctors, barristers and psychologists (although not exclusively so). They also provide advice and guidance to professionals, who do not have unions.
In any case, how exactly would a pilot act 'unethically'? Most professional associations regulate their members' dealings with money, confidential information, conflicts of interest and the like. While a pilot may make errors or be poorly trained (which has already been discussed) I don't see where the ethical judgements come into it.