This video shows pretty close to what my boy was doing when I first got him home. He wasn't quite
as bad though, but pretty close, and he wasn't as crazy e.g crashing into the roundpen fence
Same sort of senario too, in that he would look all calm while you rolled down the stirrups and put your foot into it. It was only once your weight was in it that he would explode.
Once I managed to get on him though, he gave up, fight over in his mind. He's tried it unsuccessfully a couple of times since, but he's generally fine now.