My definition of having thick skin revolves around being able to correctly receive criticism and feedback, while still maintaining a level of composure and collectedness that is professional. It is incredibly important for any job, especially one that involves hundreds of customer interactions per week. The harsh reality is that no matter the circumstances, there will always be that one type of customer which you don't see eye to eye with. As long as you are able to compose yourself and take what is being thrown at you, you will always have the confidence to come to a solution and eventually continue on to the next client.
I have shown thick skin throughout just about every shift I have worked at Apple. Apple has perhaps the highest customer expectations out of any company on the planet, and when something doesn't go their way it certainly gets voiced. Whether it be in person, or while answering phone calls, I have stayed composed time and time again and ultimately have been able to come up with a solution that keeps the customer happy.