Well it has already been said. By receiving a bird as a present, you were not able to meet it and find out if it liked you. Now you have to earn its trust and affection, and that may take many months, or may never happen. Your girlfriend obviously meant well, but she made a mistake in thinking that these cockatoos will just get on with anyone. They are highly complex and emotional birds, and are very careful about their choices.
You also took him from his best friend. Personally I only ever take Toos with their best friends/mates, because they need another bird around!! How would you feel if your girlfriend was taken away from you? Wouldn't you throw your food around and bite too?
So now you need the patience to earn the bird's affection and trust. Try to avoid "taking" it out of the cage. Open the door and let him come out as he wishes, or not. Sit nearby and chat. Sing to him, talk to him. Apologize for not giving him the chance to choose you and approve you.
Food throwing can be caused by
1) Your bird wants to let you know he is annoyed with you;
2) Your food bowl is too small for him to search in;
3) He doesn't like the food you are giving;
4) His cage is too small;
5) You took him from his best friend.
etc etc etc
Think of him as a 2 year old HUMAN. Work out how to handle the food problem as if it were your little son. Give variety, and try to find out what he likes that is healthy too. Try cooked food served warm - in my experience even the toughest cockatoo starts baby whimpering with pleasure when tasting warm food.
I am feeding my new rescues a cooked mash served warm, of a mixture of cooked grains, seeds, beans, squash and other veggies. Warm food can help the bonding process.
Try to avoid an argument with your girlfriend over this - she made a mistake but meant well. Just make sure she realizes that now you have adopted a CHILD, you will need to devote a lot of time and energy to him!!!!!!!
Oh yes - no shoulder rides!!!! Toos who spend their time higher than your eye level usually assume that they are the alpha males or females, and tend to order YOU about!! The biting is all about showing you who is boss.
OK so now realize you've not only adopted a CHILD, but a child with emotional PROBLEMS!!!! If you can now win his trust and love, it will be very rewarding.