Deal with the public for a few years. Maybe then you will understand why they have bad days.
The one local place I have been dealing with consistently for over 7 years is not like this. I have NEVER seen the owner be anything less than friendly and polite and in good spirits, and the same goes for the staff.
Bad day or not, if you're a professional and a good business person, you will not take it out on your (potential) customers.