Rude employees are rude for a reason: you allow them to be.  It's not their fault—it's yours.  You hired wrong, you trained wrong, or you coached wrong.  Just as you must kill an aggressive cancer by nuking it with chemotherapy, you must eradicate rudeness by displaying a zero-tolerance attitude.  We don't care if an employee "makes his numbers" or excels at some other aspect of his job.  If he's rude, he has to go.  Fire him, and for good measure, encourage him to work for a competitor.

- Roy Barnes and Bob Kelleher, Customer Experience for Dummies

While this tip from Barnes and Kelleher seems to be focusing on the negatives, it's actually just the opposite: it is all about removing negativity (especially rudeness) swiftly and definitely from your business so you can put your time and energy where they should go, on improving the positives.  In this manner, just like cutting off the dead parts of a plant so the remainder can flourish, you give you and your team the environment to breath and grow.  It can be especially hard to do sometimes (as they suggest, perhaps this person contributes strongly in some other way, or you have a sentimental attachment, or you just don't want to be the "bad guy"), but in the end, it is certainly worth it.  If you've never been in that situation personally, ask some other executives.  You'll definitely hear a lot of regret—not for letting the employee go, but for "I just wish I had done it sooner."