I think the annoyance the OP, and others, including me allude to - is it isn't just the annoyance caused by an annoying brat that's bad. Most people can understand and tolerate it, it's a kid after all. It's when the parents do absolutely nothing by way of effort. The lack of effort seems to amplify the outrage and magnify the annoyance whereas the slightest effort seems to muffle it. Effort seems to bring with it sympathy for the brat owner. It is the implicit selfishness of being the adult responsible for a brat whilst abdicating all effort for minimising it's effect on all others.

That's what does the temperature.