Oh, I would love to think I always treat people the way they (not I) want to be treated. But I am only human, and I know I don't always measure up.
My husband and I sometimes have to remind ourselves of our differences. When he's upset and walks away, he wants to be left alone, if only for a few minutes to calm down. If I'm upset and want to walk away it means I want him to chase after me. Childish, I know, but I recently realized that about myself.
I think I strayed off topic, so to really answer your question ...
I think it's important to really try to treat people with respect, no matter how they treat others. That being said, I know I often fall short of the goal.
When someone is very disrespectful towards me (and I mean consistently, not once or twice or on a bad day) I still try to treat them with respect but keep my distance.
One of my coworkers was very disrespectful towards me my first year. But I had to work with him 5 hours each day. So I chose to be polite but keep my distance. It wasn't easy, but I liked all other aspects of my job, had earned the respect of my other coworkers and needed the money. Over the past 18 months he has improved greatly. I still keep my distance. I am polite and try to joke with him when I can, but my guard is still up. Nevertheless, he is a human being who deserves to be treated with respect.