Most bad behavior with little ones I will ignore unless it is aggressive behavior(biting kicking striking etc) or gets really bad(running over the top of you dragging you around pushibg you or manipulating you physically with his head etc).
Baby tantrums go away. First time mistakes are forgivable unless you let them become a habit. For example. I took my now-yearling into the crosstie area the first time where we were just standing and I started a little grooming. After about a minute he decides to walk out. I didn't do anything but follow and stop him gently. I then asked him to come back in the cross tie area again. We stood for a bit more and we went home. That was very forgivable. Yes it was wrong. He should not have walked out on me, vut fixable. It won't become a habit and babies are a walking mistake. Rare is the colt that knows all the right answers and makes no mistakes.
There are lots of things you can do in a very short time frame.
If you are working with him at all off the line out in the paddock or pasture or pen or whatever, if he wants to be with you that is great. If he wants to be with you and wants to be a jerk about it, send him away. Chase him off a ways to where you feel safe. When he is being polite invite him back in. You want him to want to be with you so make yourself that person. Exploit itchy spots as much as possible but don't let him be a jerk.
Babies learn real quick how to read your body language. You just need to learn how to control it. Emulate the energy you see in a dominant horse over a young belligerant horse. When horse B is being polite amd respectful, horse A is relaxed lazy and calm. Equivlent to us leaning on the fence havin a conversation. When horse A needs to reprimand horse B it is ears pinned hard eye tense body to the point of kickibg and squealing. Think of us shoulders back head up and glaring, chest puffed out leading up to whacking and yelling. You need to be able to turn that on and off.
They also learn real quick that we are very vocal animals and learn the tones of our voices.They know when you are happy,angry, calm, tense, or bluffing. They can read you better than anything. Learning to communicate goes both ways.
A lot of his pushyness could go away without an actual punishment with consitent and proper handling.
Rewarding good behavior in my experience has always had more effect overall than punishing bad behavior. And always remember to never punish more than the mistake.
For example. If he wants to crowd into your space while you are standing block him from it without really reacting emotionally. Tell him where he is supposed to be and reward when he does the right thing. Even though he knows how to lead, give him a job of it. Lead in a pattern and then stop and stand. If he has a baby tantrum safely ignore it until he does the correct thing. It sometimes takes stopping and asking again. They are just figuring stuff out. Right and wrong is a new concept and "that is right" is easier to teach than "that is wrong". I teach all my babies the job of a futurity baby whether or not they are shown. It gives them a sime job they can focus on and you a goal. We trot in hand down the barn or outside and stop and park out like they are supposed to. You could do this by walking from A to B, trotting from B to C and walking home. Who knows where you will lead this colt or what speed it will require. Leading lessons and games are very valuable.
. If he is crowding you while turned loose, a very dangerous thing, just drive him out of your space. Clap your hands, wave your arms, make him uncomfortable to be that close. You are the fun wonderful keeper of the almighy wither scratches. You are a good thibg that they want to be around. They need to learn that they have to be polite if they want scratches. If not they have to go away and they don't like it.
My two yearlings are funny. They beg for attention and scratches all day long but theu can get a little demanding or jealous of the other so they get sent away until they want to behave. Then I allow them back near me. They don't get to make the rules. They are rotten rats to the core but they have to behave. I have never once hurt their feelings by chasing them away and never once have they refused to come back to me or let me go to them.