Bro Blocking is a fine art in which one of the male gender stops another male, or bro, from doing something cool.
"Chad was totally bro blocking me when I tried to play guitar hero. I was about to plug it in when he turned on Elton John live in concert".
The opposite of cock blocking. When some one prevents you from chilling with your bro(s).
Tyrone: Damn, dan never chills any more...
Jamal: That greasy bitch hes dating is bro blocking.