From years in the service industry I can assure you that some people just get off on yelling at other people. They can't yell at the average guy on the street or they would get punched in the nose. Same thing if he yells at his wife. So they often go off on someone in the service industry { sales clerk, waitress } knowing that 9 times out of 10 they just have to stand there and take it or they've lost their job.

My opinion of folks like that is not very high. They are bullies.