How to warn an employee who has been behaving inappropriately with junior employees, due to superiority? Also, how to avoid such happenings?

I would recommend having this matter discussed with the individual by his/her immediate supervisor without the knowledge of any of the other employees. Should the unacceptable behavior continue, it should be brought up before the HR. 

let the superior straight know that his/her behavior is not the apt way and very unprofessional. Even after that the superior doesn't mend and behaving inappropriately, give information to the HR and through HR to his line manager for remedy. Thanks.