First You need to spend time in the same room at a distance where he doesn't have his beak open in a "threat display". Then side in the room and speak to him, it doesn't really matter what you say, just get him use to your voice.
Also approach the cage slowly, avoid all quick movements, show him you mean him no harm.
Next try to offer him food treats, you might have to place them in the cage at first, then slowly get him to take these treats from your hand, but this might take weeks or months.
It can be so worth while once you get him tame or even semi-tame.
Some birds are just plain nasty. Don't hold your breath on the other's suggestions.
dress up like the previous owner and stay like that forever.
My old lonely great aunt taught him to be literally as loud and irritating as possible. And to make matters worse, I can't even touch the cage without him going into attack position with his beak open. I've never had a bird before (thank god I love with two sisters and a mom or I might've killed him by accident) and I don't know what to do. What can I do for him not to hate me?
