Unbrofessional is when one of your friends does something that might require you to take their man card away from them or they do something to break the bro-code.
Situation 1: "Dude, I can't believe you told her that I was checking out her ass. That was unbrofessional."
Situation 2: "I was talking to that girl and you came over and just stood there smiling, looking like a dork, and made her leave before I could ask her if she had a boyfriend. That was very unbrofessional."
Situation 3: "I can't believe you cock blocked me like that, you unbrofessional assclown!"