How frustrating for you.You don't know how rude some people can be until you've had a job dealing with the general public do you? I know I've had to bite my tongue on a few occasions at work when people have become abusive.I say to them something like 'I can understand your frustrations but please don't speak to me like that,I'm doing my best to help you.If you carry on with your abusive language I shall terminate the call.'
I deal with customers over the phone rather than face to face you see.Keeping calm and assertive usually has the desired effect and they calm down.If you're lucky they might even apologise! It's not easy though when you just feel like telling them to shove it,I know.
