I regularly get apologised to by customer service people when I have been waiting for coffee of food. Usually something like "Sorry for the wait". While I am

I regularly get apologised to by customer service people when I have been waiting for coffee of food. Usually something like "Sorry for the wait". While I am waiting, I often retreat into my own thoughts, mentally processing some difficult problem or trying to plan out a project in my head. When I am thinking hard I adopt a "focus" face with a slight frown with lips pressed together. The servers must be reading my face as annoyance or anger. I always say thanks and smile when I collect my order so they know I wasn't unhappy, especially with them. I guess most people are more "in the moment" and maintain a neutral or friendly face.