I think you may need to give the colt some "tough love"
Often orphan foals are extremely spoiled and will walk all over people, and it only gets worse with age. You'll need to make sure that you are the boss over this colt. Too much coddling is a bad thing.
Do you have a babysitter horse that you could turn him out with? Since he doesn't have a dam, he's going to need another horse to correct his bad behavior and put him in his place, show him how to respect.
I too, am wondering how old he is. Might be time to geld?
"The greatest pleasure of a dog is that you may make a fool of yourself with
him and not only will he not scold you, but he will make a fool of himself too."