auto-bro
You know you have your bros (your best friends, etc.), but an auto-bro is someone who is nice, funny, and outgoing right when you meet, up them until death. They are the kind of bros you wanna joke around with, and so even though you may not know them well at first (therefore not getting full bro status), they automatically take some sort of bro status.
One of your bros: Hey do you know that guy? He seems cool.
You: Yeah, he's cool, but I don't know him well enough. He's an auto-bro.
You: Yeah, he's cool, but I don't know him well enough. He's an auto-bro.