I have a lot of experience with stallions. Unless you've had stallion experience, I don't think people truly understand how quickly their behavior can change when hormones are involved. :roll:
I use a chain, always. A chain can be very kind in gentle hands, but I've also seen a chain make a horse's mouth bleed.
For example, a mare once got loose as I was walking a stallion out to his pasture. This stallion was aggressive and had been taught no manners by it's owner. Regardless, as the mare ran past, the stallion that I once easily controlled then reared up, jumped forward and drug me with him. I was basically flinging around by his side without him paying ANY attention to what I was doing. The stallion was solely thinking one thing - mare. Yes, I had the chain in his mouth which did slow him down a little, but I wouldn't have been able to stop him unless someone had ran over to help me. If I had just a halter on I would have probably have been trampled. It happens quickly and powerfully. This was an extreme situation, of course. But, this also leads to breeding. Breeding a horse without a stock to hold the mare can be extremely dangerous due to their behavior. An experienced handler should only do this with care. Using a halter on a misbehaving stallion while in the process of breeding isn't the best option. You need better control.
I should also add that I use the chain differently depending on the stallions bad habits.
There are better stallions with very kind manners. I still use a chain. With these guys, the chain is not jerked or used roughly, rather in neutral. This is not painful when used kindly but it is there in emergency. I've found the chain useful on stallions that like to nip. Having the chain to chew keeps them occupied.
But, having a kind stallion leads to manners as well. It is essential to discipline any horse that proposes a threat or safety hazard. A stallion cannot be dealt with too aggressively, but nor can any horse, really. I have had to become very aggressive before, but I knew my limits and the horse well. But this didn't guarantee anything and it's not something I recommend. Sometimes creativity must come into play when working with a stallion. For example, with the nipping, a chain or lead to chew may keep them occupied. Or, rather then hitting, a squirt of lemon juice in the mouth right after they nip may cure the habit. It just depends but in no way should a stallions bad manners be ignored because 'they're just a stallion.' It's not an excuse!
The going stupid near other horses thing may not be curable. I understand those moments too well. They can be worked on but the excitement of hormones can be over whelming at times - for both the horse and owner.
But I do completely disagree with the fact that if a stallion does this, they don't respect you. Horses have short attention spans, are deeply set in their ways and can easily jump from thought to thought. I just didn't want you to think it was a fault of your own if they did this.
But don't worry! Things will progress! I have seen some lovely stallions that I swore were gelded. Not all are mind numbing and vicious!