Before you give an example, think about what excellent customer service means to you. Does it mean making the customer happy? What skills are required?
"A customer called to make a reservation for a large group. They were visually impaired and there were two small children in the group. I wanted to take extra special care to provide for their needs, so I informed the server and made notes in the reservation. When the group came in, I was warm and friendly. I made sure they were taken care of."