If it something he is doing to YOU. He does not respect you. Since you had him @ a trainer who got along with him well, ask them. It might be something as simple as your body posture. If you stand up straight keep your head up and look him in the eye, he is more inclined to think you are dominate. If you look down, slump your shoulders, talk softly try to be his " Oh, Its ok, nothing bad is going to happen" friend he will walk all over you. If he's fed in a stall- Go in put the feed in his bucket and leave, BUT
If you go in and do just that-You think here you go buddy. He thinks- I've run her off again.
With mine I teach the word "round" When I go in the stall I tell them round they turn and face the back of the stall, I dump feed, exit shut door and aproach the next stall then use their name and ok, they can then approach the feed. If I change my mind and re-approach and use the word round they will leave the feed and face backwards.
If you can get that kind of control, you really shouldn't have other bad behaviors-Just time and patience and consistant repitition.
It doesn't have to be over food, just an example.