Cutting in line, speaking offensively and playing music loud (the general types of offenses under discussion) are all offenses without a specific target. That is, until someone makes it about them and the offender, there's no confrontation.
If a person, or group of persons singles out a target for their attentions, a confrontation is already created, and while, by the letter of the law, it takes more than words to rise to the level of an assault, a group harrassing a defenseless person is, at best, within a hair of breaking the law, and could go over that line at any time by doing something as simple as shaking a fist or even just making a sudden move toward the target of the harrassment.
In other words, while you deserve kudos for dreaming up a hypothetical that's so creative, it's not at all in the same vein as the focus of this thread has been up until this point.
That said, even in the unlikely event that this hypothetical group of young men were so circumspect and well-informed as to stay strictly on the legal side of the law; I think it would be more than reasonable to summon the authorities to the scene and, until their arrival, keep an eye on things to make sure that they don't get out of hand.
If the target of the harrassment reasonably appeared to be in real danger and the authorities were still not on the scene, then there would be another decision to make, namely, am I willing to risk my well-being for the benefit of the defenseless target? However, at that point, we've clearly crossed the line from legal to illegal behavior.
