I'm sorry but that is something that is eventually going to get you hurt pretty bad so he needs some stern discipline.
I once had an adult, 15H, gelding try something similar but he only did his crowing at feeding time. His third attempt was his last one because I was ready for him with a 1 X 2 board that my 5'2" white female self roundhoused with everything in me, connected to the fat of his hindend and broke the 1 x 2 across his butt.
I hadn't realized the board was on the rotted side or it would have never broke; I almost went around twice because of that
It turned out to be a double lesson as my 12 yr old son witnessed all that. Wide-eyed at the feat his mom had just performed, he said "wowww mommm! You broke that board over Dazzle's butt!!"
I whirled around and said "Let that be a lesson to you"
I couldn't have that horse playing those games because my son was at the barn as much as I was, so discipline had to be hard and fast.
That was the last time that otherwise well-mannered horse ever tried to crowd.
Point-being, I would wail the hind end of that colt one time, really hard, adding a big resounding "NO!". You can't hurt him near as much as another horse would.
If he's not gelded yet, that might be a good reason for his butt-turning antics. He may be ready to have some of his family jewels removed