Well... in my opinion, being an photographer but was unprofessional, I think we need to come up with assumption that the photographer is earning a profession by taking photographs (of any genre) and also maybe giving advises and consultation to other people (in regards to photography). However, he/she was not too ethical in his/her approach, gave wrong advises, being late for projects, doesn't dress to the occassion when doing a paid job, being sloppy in his work, give half-fxxk result for his work. well... that is unprofessional photographer.
Other people who know nothing but think he/she know the world and attempt to give advises (bad advices, or totally wrong advises) is at most acting smart and is truely irritable. Copying others' work or claiming credit for other people's hardwork is in a sense unprofessional (as in unethical approach to work) but can also be seen as cheating his/her clients and can be sued.