Buster is my bad boy here. I picked him and his cage mate up several months ago and as soon as I moved them into the chin room with the other boys he went psycho. I leaned close to his cage one morning and he lunged at me, scared me and made me spill my coffee and his behaviour just got worse. He'd make all kinds of grumbling/growling noises, bit me constantly and generally was just an angry and no doubt scared chin. There were times when he was out for playtime in my chin room that he'd run around, circle the room and then jump on me and bite my arm. After that I just stood up while he was out and kept my distance from him.
Neither of these guys had ever been around other chinchillas before and I really do think that was/is part of his problem. He even started picking on his cage mate of two years and I ended up separating them b/c I found little bite marks on Rupert's ears and his fur was really scruffy.
I think I've had them about three months or so and things are so much better with Buster. He seems to like not having to share a cage with Rupert anymore and he thrives on a daily routine of me tending to the chins, cleaning up and letting each one out for a runabout and a dust bath and then back into the cage with a little pinch of oat supplement as a reward for going in for the night.
Before I had him 'trained' so to speak, to go back into his cage by himself, I'd put on leather gloves and scoop him up b/c I didn't want to get bitten. I actually haven't used the gloves in weeks now so that's good. When it's his turn to come out, all I have to do now is go up to his cage (no more lunging) and ask him if he wants out, he gets all excited and hops onto my shoulder, I give him a smooch and he runs down my back and onto the couch.
I can also sit comfortably on the couch and have him bounce around the room without him lunging and biting me which is huge progress but now he's actually having fun instead of stalking me.
I'd say time, patience, perseverance and a good routine is what you have to do to tame these wild ones and a pair of gloves helps too.
This is my not so bad boy now Buster and notice the gloves on top of his cage. The little guy on top of his roof is his ex-cage mate Rupert who on occasion does find his way up there but I quickly take him down b/c I don't want his toes or nose to get nipped.