As someone who works in a service business, I will tell you this - you are only hurting yourself with the rudeness, because when someone comes to me and needs my help to fix something or to do something for them, I expect at a minimum civility while asking me. Any rudeness to me or if I hear of rudeness to anyone else will get you only what I need to do to keep my job.

I think knowing for certain that if you are rude to someone you need to do things for you (treatment, scheduling appointments or tests). you will get the bare minimum and there are people out there who will sabotage you just to get even. Try smiling when you are talking to people, it makes your tone lighter and more pleasant when speaking. This can be done in person or over the phone.

Please know that I am in no way saying you are not allowed to have feelings about certain people - YOU CAN. Just hide it. Things will work out much better if you do that.