Ok, sure, if you've only worked adjacent to kids or in one-on-one environments you might still be that naive, but even the most compassionate and sympathetic teachers experience it by the end of their first year - all children misbehave in a wide variety of ways for a wide variety of reasons and thinking yourself above getting annoyed by it is setting yourself up for failure.
You don't actually do it, but you definitely discuss it with your coworkers over lunch on particularly bad days.