While these stories disappoint me, I am not surprised. People that exhibit poor behavior at work or at home aren't likely to change their spots on vacation. Unfortunately, when we walk away and/or don't tell someone, we reinforce the behavior. I'm not saying anyone should continue the confrontation, but
I've found that with Disney if you summon a cast member, they usually do a pretty good job of sorting things out. Of course, I've also seen CMs become the victim of some pretty harsh confrontations, so that doesn't always help, but it does help clarify who the troublemakers are.
I've run across these people a few times. The queue of Casey Jr.s train at
Disneyland, the queue for Splash Mountain on Mother's Day, waiting for the Pirate show on the Wonder and hunting for tables in Cabanas. Conflict is initiated when one party feels they are being victimized in some way or they are already behaving badly and don't want it pointed out. It's hard to know what drives the behavior.
Over the years I've observed there are three things that people will defend vigorously. 1) Their family (kids), 2) Their money and 3) their time. Any perceived threat or challenge to any of those three and there is a potential for an issue. Disney Security has a reputation for handling unruly guests quickly, which is often enough to discourage poor behavior.
As for spray sunscreen. I love the stuff. I used it on the balcony of my cabin before ever leaving the ship. It's usually most effective when applied prior to sun exposure. When it comes time to reapply, I try and find someplace away from everyone else and I pay attention to the wind. That isn't always possible if you are dealing with multiple kids all in different situations, but there is no excuse for becoming aggressive if you accidentally allow some to blow onto others.