I manage a medical office and quickly found out you can't please every customer(patient). The majority are wonderful. Don't let the one SOB ruin your day or your smile!! You seem to have a good positive attitude and this is reallized by your customers and they (generally) reflect this back to you.
Just keep smiling and when you punch out at the end of the day get in the car with the music turned loud and DON'T rehash all the bad things that happened. Leave them at work--tomorrow's another day.
You sound like someone I'd like working for me or waiting on me as a customer!!