It is absolutely a respect issue.
You have to use severe enough negative reinforcement to make him NOT want the consequences of being that bad mannered. The consequences have to outweigh the pay-off for the habit he now has.
It may have started with a bad fitting saddle or it may have started when he did not respect someone, did this and they did not finish saddling him up that day but decided to just do groundwork instead or turned him back out. Whatever, he won a round and will not give it up without a good enough reason, now.
I can tell you that barely pecking on him and scolding him will not only NOT work to fix the problem but will probably make him get more bold and meaner. You have to punish him severe enough that he DOES NOT want to do it again.
When I had horses brought to me for this kind of behavior, I would put a chain lead over the horse's nose and 'set him up'. I would not even throw a saddle pad on him. I would take and old 'junk saddle', walk toward him with it, and the instant he laid his ears back, I would throw the saddle down and jerk the chain lead 3 or 4 times VERY HARD.
Then, I would go back to the saddle, say "Whoa!", pick it up and try again. After three or four of these responses to his threatening posture, he would usually stand there and let me throw the saddle on him. But, he would probably put his ears back and threaten to bite when I reached for the girth. I would jerk the saddle off and punish him again. It would not be long before he fell in love with being saddled.
Then I would take him to the tack room and put a good pad and a good saddle on him. I would be ready to punish him again if he did so much as lay an ear back.
After getting him back to being respectful, then it was time to have his owner start handling him. They oftentimes try it again with their owners. They had to learn to respect them and not just respect me. They did not have to get after him and roughly as I did, but they always had to get after him enough to make the horse behave for them, too.
This same routine works for horse that kicks or threatens to kick when saddled or groomed or for about any other threats or expressions of really bad manners that can be dangerous.
I cannot over-emphasize that just mildly scolding or pecking on one will make many of them worse. Most of the truly viscous horses that I have had to re-train that actually attacked people started with behavior like this and it escalated to attacking, charging, whirling around and kicking viscously, etc. Pecking and scolding just does not stop this kind of behavior.
Remember, if you punish or scold a horse for something and you have to do it every time you try to do the same thing, you are not fixing the problem. If he has trained you to take two people to saddle him or you have to tie him real short to keep him from biting you, you are not fixing the problem. If you are just barely getting past him each time and are just waiting for the problem to get worse, you need to realize that he is training you instead of you training him to be a happy, well-trained horse with good manners.