I hate to be this blunt to someone on their first post and it is not much of a welcome but in defense of the horse, I must say what needs to be said.
You own his aggression and behavior, 100%. This horse does not need to be put down or 'laid down'. He just needs a competent handler that will kick his spoiled butt before he fully earns his trip to Mexico.
His story reads exactly like most of the spoiled, mean horses I used to get in as 'public trainer'. He has been picked at, pecked at, nagged at until he has gotten really fed up with you. You can make any dominant horse mean by pecking at them instead properly disciplining them when they first need it.
When he was just being 'nippy', he was testing you and you came up short.
If you have to discipline a dominant horse more than twice for any aggressive behavior, you have failed and have just made that horse's resolve stronger! This includes anything from biting, to laying back ears to trying to kick or paw at someone.
Screaming and yelling is not discipline to a horse like this. It needs to hurt. Plain and simple, it needs to be a painful deterrent. It is way too late for that kind of 'mannering'.
This horse has 'bullied you' many times before he attacked you and you stepped back instead of stepping up to the needed response. Now, he has progressed from pushy and obnoxious to dangerous. It would take a competent trainer less than a week to turn him around, but he would go right back to pushing you around as soon as you got him back if you don't learn to 'read' a horse and come up with the correct response.
When people let horses get this ill-mannered, they doom most of them to the slaughter bound truck.
I used to straighten out many of these horses, but I would not do it unless the owner came and let me straighten them out with the horse. Without that, most of them would go back to aggressive behavior when their owner started hugging and kissing them and treating them like a dog instead of a potentially dangerous horse. Once you start making excuses for the little things they do, it is all downhill from there.