Why is customer service so hard for some people??

So I had something happen today that confirmed my reasoning to start my own shop up.  I had to go to a competitor’s shop today to pick up a part – we have the same supplier so it was a simple transaction.  Two of the people there that I have known for a while were very cordial, asking about my shop, comparing notes and the like.  But the gentleman helping me was well, to be honest, not exactly polite.  In fact, downright rude I thought.  Over a ~$30 part.  I was completely caught off guard and really didn’t think much about it until I was back in the Raptor on my way to my shop.

If I ever get that way, I expect someone to call me out on it and slap me across my face.