it's a great word when used at the right time, but at the wrong time it's totally out of place. (I am guilty of this on occasion)
disclaimer: I'm about to go STJ for a moment
appropriate times to use bro: with family, with close male friends, with someone you're sharing an intimate (non sexual) moment with. for instance "my mom died" "it's gonna be okay bro, I'm here for you"
inappropriate times to use bro: in a formal setting, with someone you don't know (omg I hate this lol), in a business setting (though it's not inappropriate in any professional setting. if you're working on a movie set, it's not weird to call someone bro)