I have a male 8 month old staffy called Blue. He can be very friendly with new people and strangers, however sometimes when he is with me or my family he will unexpectedly turn and become aggressive. He can be nice and calm (although most the time he is hyper) but then suddenly he will be barking, biting and growling. He only does this with me and my family and has been doing it for a while. He also doesnt get along well with other dogs. He has already bite my mum twice and drew blood, and tried attacking me. 10 days ago he had an operation to remove his balls since they hadnt dropped. Is there anything i can do to stop this behaviour? Or is my dad correct in saying he is a 'bad dog' and we need to get rid of him.

Get a behaviourist in, one that deals in positive reinforcement and NOT 'dominance' or pack theory.  Sorry, but this is a situation that needs eyes present to see exactly what's going on; it may be that he is playing - I see quite a few dogs at about this age who bark and growl and bite and it's all play, but seriously OTT from a total lack of self control.  That can be worked on but you need someone knowledgeable to tell you exactly what is going on to start with - whether it is that, or if it is genuine aggression and why.

Some things I will ask though: what are you feeding him on?  What's his daily routine?  How much mental stimulation does he get - training, interactive toys (treat balls, kongs)?  How much play and what sort of play (chasing balls, tuggy etc)?  All of these things can have a direct effect on his behaviour.

We feed him meat such as cooked pork and meat from pigs heads mixed with puppy biscuits from eukanuba. His daily routine is we try to walk him at least twice a day but we havent recently due to his operation, however he runs in the garden and has a variety of toys. He goes dog training on  monday and can sit, stand, lay, give his paw and jump. When we play with him we tend to play fetch and run with him.

How long has he been doing this behaviour?
I'd also get a full health check done on him in case he has a medical problem.