Model Cheerfulness

What do you do when you encounter unfriendly service people?  (For example, someone in health care.)  Initially, I feel disappointed, that this person chose a career in serving others and then greets me without a trace of a smile.

Then, I am inspired, when I encounter these people, to be engaging and kind.  I move past my disappointment at the sour face, and choose to be warm.

When my children witness an encounter with an unfriendly person, I instinctively want to shield them from that person.  Knowing that they will meet and engage with all types of people, I choose to model kindness.  

What do you do when you meet people who are reluctant to smile, matter of fact, and do not exhibit warmth to your children?