Scene: a public place. A child-not a toddler, but an 'old enough to know better' kid- and at least one parent. And you. Said child does something awful...throws an absolute hissy fit, repeatedly kicks the back of an airplane seat, licks the food for sale in a retail case. Said parent does....nothing at all.
What do YOU do? If you can honestly say you don't judge the parent just a little, then you are a better, more charitable person than I am. Even worse: it's your kid. You wish the floor would open up and swallow you, because you KNOW you're being judged.