He's already got spoiled syndrome.... Don't feed him any more treats!
This aggressive (some one said it's not aggressive for a donkey to bite and bully you which is a crock, because that IS aggressive) behavior needs to be stopped for your saftey and everyone elses... you don't want him to bite the hand of a small child, or rear up on, or start kicking people because they aren't "Serving" him.
I know, because my dad bought a Donkey like this from people that continued to spoil him a little bit beyond the point that this donkey is at. And one day I was in his corral cleaning it..Everything was fine until he wanted treats that I didn't have.. and he tried to kick the crap out of me. Rearing and striking out with his front hooves, and biting at me like I was another Donkey.
It took several MONTHS of intense "no food treats" and behavior correction to get him into a managable condition.. You NEED to start teaching him that petting is just as good as a carrot or an apple or sweet grain.....If you don't... expect to get hell on four legs ATTACKING YOU!
Donkeys are extremely smart and know how to take advantage of situations. If you want a lovable friend/companion lay off on the treats. And once he becomes well mannered, put his once in a while treats in a bucket, or include everyday treats with his regular feed. That way he takes his aggression out on the feeder and not you when he gets pissed..