Q. "Can I address immature and unprofessional behavior without it sounding personal?"
Answer:
Yes, we would suggest first giving the employee a verbal warning concerning any unprofessional behavior.
Since "grow up" may not be the most useful advice, you can tell an employee that their behavior (i.e., slamming doors, stomping, etc.) are not acceptable behaviors in a professional setting, and that you would appreciate it if they addressed frustrations with thier direct supervisor or with you. Remind the employee you’re on the same team, you want them to succeed, and that they're not alone.
If the employee continues to display the same type of behavior, we find it best to pull the employee aside in that moment, let them know this is an example of unprofessional behavior, and warn them further discipline will occur if the behavior doesn’t stop.