I think there is something about 'bro' that is accepting and welcoming. Like in the african american community while growing up, not so much today unless you're dealing with someone from the older generations, I was use to being called little bro, little brother, hearing girls be called sister. Its a way of relating someone to yourself. nothing awful about it.
I say dude, bro, man, sir, guy, all of them. I don't over use them, but for people who do it doesn't particularly bother me.
But you are speaking to a guy that grew up during the "like" phase.
I don't see why it should such an awful thing though. My family says ain't. Sometimes I say it. I would think it a shame for you to not even aknowledge me if i wanted to speak to you and used the words sup, or ain't. Does that really make people so low?
For those of you so quick to judge someone's sophistication and class based off of such trivial observations, you may miss out some great friends and great networking as well. Just a thought.
CULTURAL RELATIVISM my friends. In my career I have no choice but to have it most of the time.