Dear Student,
Thank you for letting me read your cover letter today. It is an excellent example of quality and thoughtfulness. I especially appreciated that you are applying for a "social position" and that you are looking forward to working with "mentally ill and psycho people". There is not a more professional or eloquent way of phrasing your interest.  I know that your degree in Behavioral Science has done an excellent job in preparing you to work with psycho people. I know working in this department has helped me.

Good luck in your search.

Sincerely,
Me