Experiment #5 on Flickr.
I admit I’m cheating with this one, because brutal politeness has been my weapon of choice for years.
Note that I don’t mean “fake niceness” where you are saying “go to hell” with a smiley face at the end. Nor do I mean “be a doormat” - niceness can mean saying “no” but with class and self-possession.
I mean civility! Be, in other words, a GENTLEMAN. (Regardless of gender.)
One of two things will typically happen when you deploy this brand of niceness: the jerk will suddenly realize that they’re dealing with a human being and cool down; or every other witness to the interaction will remember how the jerk threw a tantrum while you acted like an adult.
And, if the interaction was a private one, you have the satisfaction of knowing that you behaved well. Magic!