I'm not from the US, so I'm surpised it is so normalized, that someone - who is not a member of a gang - would carry a knife in his swimsuit for an afternoon of fun and drinking on the river.
IMO, wherever men routinely carry knives, stabbings are inevitable. Male honour and pride is so easily wounded. And if the man believes he doesn't have to communicate with others to diffuse a situation, because he can always just stab them, he doesn't use ordinary communication, he doesn't even threaten them with the knife to get them to back off, he just passively waits until the insult goes far enough, and then pulls out the secret weapon and kills.
JMO