What's the best way to fire one of my employees?
Also, one always needs to carefully consider whether one is firing someone for sufficient cause/good business reasons and that one is not discriminating--consciously or not--in any way.
Are you making this decision based on facts or conjecture/impressions/insufficient data? If it is the latter, you will regret it. So, think it through carefully.
If after careful analysis you believe that you have an employee whose behavior is disruptive or otherwise consuming company time and energy disproportionate to his value as a producer, you can terminate his employment.
If you have a performance review process, you should use that process and form to record your impressions of this employee's behaviors that are objectionable in an organized way. Regardless, you should prepare for a meeting with this employee by itemizing for yourself the issues that are bothering you. Including dates of infractions/incidents will help you to put together a chronological account of the myriad of ways in which this employee has brought you to the point of being ready to dismiss him.
Arrange to speak with him in private at a time of day when you will not be disturbed. It is a good idea to have someone else in the room with you when you talk with the employee. Tell him what your impressions are of his work record and then do one of two things: terminate him immediately or give him a period of time to improve his behavior.
If it is the former, be prepared to collect company property and get him on his way. Be sure to pay him for all time worked in a prompt fashion. If it is the latter, be sure that he understands exactly how to improve in order to keep his job--and meet with him at least weekly for a while to discuss how he is doing and to reinforce the necessity of good job performance and good work place behavior.
With any employee action you should document what you did, why you did it, when you did it and so forth. A few months--or even weeks--later it may be very hard to remember exactly what transpired.