Not going to lie, I wouldn't put up with that. People send horse's to my trainers who have bad behavior about things like that (but not just like that haha:) ) And he fixes that. He doesn't abuse by any means, he just basically shows them who the boss is and doesn't let them get away with it. Try sending him to someone like that? He seems like a nice horse in the ground, but if he has more energy than normal, lunging is kind of a must, I would think.
I've had mine for 3 almost 4 years and still to this day I lunge him until he's very tired. He's now 8 years old and dead broke. Otherwise, he still tries to buck or the occasional spook at something stupid. But that's just his mentality haha :)
Really, good luck with him! I'd be scared of him too!