Dear Sender,
Termination is not the right solution to be used instantly. He can be adequately issued warning letters. After having documentary evidence with you, and if he misbehaves, which has been noticed evidently, then you can go for issuing a termination letter (that too, after considering the pros and cons).
On the company's letterhead,
Addressed to the employee,
Dear,
Sub: Termination from the services
Consequent upon our verbal advice as there has been no sign of improvement in your performance and career, and the recent incident of your misbehavior with our office staff has proved that our prediction is correct. Accordingly, the management has come to the conclusion that you do not possess good character and are not willing to improve your performance. Hence, management has decided to terminate your service with immediate effect based on your poor performance and misbehavior.
Thanking you,
Yours faithfully,
For x x x x x
Regards:
You can add, if you want to settle any dues to the employees, as a separate paragraph in the letter.
L. Kumar