That doesn't sound like autism, that sounds like he's getting a little spoiled. My advice, if he threatens you with a fork, take it from him and give him a few swats, and send him to bed a little hungry. ((Or give him the choice to eat what you give him, or go to bed)) Keep indulging him and he'll get worse, and those violent tendancies need to be put down before he hurts someone.
On better days, show him nicely how to hold a fork or a spoon, and if he gets it right, reward him. Days that he's good, and eating like he should praise him, offer dessert, or a little extra dessert, for his efforts.
This may seem harsh, and you'll want to excuse his behavior, but it's best to know why he does it, but still discipline him for it. Good luck. ^^