How many times were you told to "behave" by your parents or teachers? How many times did you use the same or similar phrase with someone else? The funny thing is, no matter what a child is doing he or she is behaving.
Behave: to do something. EVERYTHING you do is a behavior. Thinking, sleeping, dreaming, screaming, sitting--if you can use it in a sentence as a verb of some sort, then it is behaving. As such, behaviors are observed, measured, described, explained, predicted, controlled by psychologists of every fashion. Our whole science hinges on overt (readily observable) behaviors and covert (not readily observed and often inferred) behaviors. To us, everything a human can conceive of, even thinking and emoting, is a behavior subject to study and potential control--especially for the behaviorists.
So, any time a parent tells their child to behave, I cringe a little and the snark in me wants to inform them that the child is behaving, albeit perhaps not in the way desired. Instead of telling your child to behave, try giving them specific directions. Even "behave well" or "behave better" gives a smidgen more direction that simply "behave yourself." Giving children, or any human for that matter, such vague directions leads to a myriad of miscommunication and misinterpretation, which leads to frustration and upset.
Do yourself and others a favor and instead of demanding that someone "behave" themselves, give them specific desirable behaviors to achieve. You can even give specific behaviors to reduce or avoid. Even Dr. Tess Coleman's (Disney's remake of Freaky Friday) edict to her daughter to "make good choices" is better than "behave."