In the new game pack children and teens can go through phases where they will act different. These usually last a few sim days. I have had the loud phase, rebellious phase, bear phase (where the sim dresses as a bear) and the mean phase, all for kids. I think your sim had the mean phase since when my sim gets it they fight and do mean interactions randomly. When your sim has a phase you can find it out in two ways:
1. Look on the notifications. Usually when your sim begins a phase there will be a notification for it.
2. Look on the simology place. Below your traits will be an extra one which is a phase.
Hopefully this will help you! I personally like these phases since they keep my game realistic. Good luck! :)