Fair and Efficient Performance Reviews

 Suppose  you were recently promoted to a supervisory job in a company where you  have worked for two years. You genuinely like almost all your  co-workers, who now report to you. The only exception is one employee,  who dresses more formally than the others and frequently tells jokes  that embarrass you and the other workers. Given your preexisting  feelings for the employees, how can you measure their performance fairly  and effectively?