General:
* Misbehave
* Act up
* Behave badly
* Conduct oneself improperly
* Be unruly
* Cause trouble
* Get out of hand
More specific:
* Disobey: If the focus is on breaking rules or instructions.
* Be defiant: If the focus is on resisting authority or being rebellious.
* Be disrespectful: If the focus is on showing a lack of regard for others.
* Be mischievous: If the focus is on playful but potentially harmful behavior.
* Be unruly: If the focus is on being difficult to control or manage.
The best synonym to use will depend on the specific situation and the nuance you want to convey.