They don't understand it. By the Arthur C. Clarke rule, it's equivalent to magic. When you challenge the powerful, you are guilty purely because you did something the average unsophisticated user isn't capable of.
Madness string 56518
I've been in a similar situation a couple of times before, and I always make a point to apologize directly to the child for their parent's 'terrible behavior'. That usually gets the shitty parent really riled up, which is always good for a laugh.