Instead of donning a red tail ribbon, train towards and attitude adjustment.

1. Set the boundaries. When your horse snarks at another horse, re-establish the boundary through which he snarked . For instance, if he kicks out, move his haunches sideways from the leg on the side he kicked.  If he lunges his head toward his neighbor, back him up. Don’t respond to emotion with emotion.  Just promptly but calmly make him work harder for every threat.
2.  Spend time creating and repeating positive experiences beside another horse. Riding beside another horse, just inside your horse’s comfort bubble and no closer. Relax your body, soften your aids, then ride away. Repeat until the comfort bubble becomes closer to his neighbor.