Well it could be sexual frustration my male cockatiel also does that and took his anger out on my female cockatiel but after I took him out of his cage he went and sorted himself out and he turned into the loving baby he used to be but it could be anything not much help but..

I have had him for over a year. I am positive it's a boy but can't be 100% certain because he is purely white. Anyway, compared to other cockatiels I have seen, he never whistles appart from mimicing my wolf whistle and rarely ever chirps. When he does chirp it is a really harsh sort of sound unlike other cockatiel chirps i have heard. However he does talk and chatter away, but it is very hard to understand. He can say who's a pretty boy (while looking at the mirror) but most the time it is so gibberish you can't make it out. And he has attitude issues. If you put your hand up to him, he will start hissing and and begin to peck at you. He has been doing this for a while now and it is becoming a bit of a problem. I have tried many things which don't seem to really help. And I noticed he hates toys in his cage. Is that wierd? Like he will never use them, so I have to give them to my lovebird. I brought him as a hand raised bird from a local pet store. I know it isn't the store because I buy all my birds there and they have all been fine except for this one.