If you're not so big and scary looking and the "smile and wave like a fool" method doesn't work, there's always the "pull out your cell phone and look like you're dialing 911" approach. That's my Plan B, and it has been effective the 4 times I've had to use it.
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"Real wars of words are harder to win. They require thought, insight, precision, articulation, knowledge, and experience. They require the humility to admit when you are wrong. They recognize that the dialectic is not about making us look at you, but about us all looking together for the truth."