I work with the public every day. I can relate. I used to be real polite no matter what. Then, I moved from Oregon to Chicago, and learned how to get in people's faces and be rude right back. Then, I learned how to be polite again. It's tough to know what to say in each situation.
I find that focus on what I am doing, and non-response to rudeness works well. Were I in a similar situation that you were in, I would simply ask the line cutters to please step back as I am helping someone ahead of them. They will need to wait. Every time they blurted out more nonsense, I would keep repeating the request like a broken record, until they moved. If they did not move, I would call security. I would never acknowledge their silly claims, and I would never defend my feelings. I would, however, remain calm, with a low voice, and simply repeat myself.
In my office we do not have security. So, I simply ask rude people to leave, and I have done it. I then walk away from them, back to my office. If I am on the phone, I tell them that they are rude, and I end the conversation, and hang up. I move on without caring one wit. It is not worth my emotional energy to give such people the time of day, much less my own personal hurts.
I learned this after my heart attack.
Jim Whitney