Mine is very simple and very contentious: It is completely unprofessional to implement a solution you've been asked for, if that solution is bad practice. Tha

Mine is very simple and very contentious: It is completely unprofessional to implement a solution you've been asked for, if that solution is bad practice. That is to say, if you're asked to make a hack that will cause pain and misery, has a security risk attached, won't be performant or other clear, obvious risks, it is unprofessional to not object and in some cases, refuse.