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One of the tactics used by arguers is to attack the source. For instance:
Professional Arguer: "Where did you get that information?"
Normal Person: "NPR, or the NY Times, or the Wall Street Journal, or Rush Limbaugh or..."
Professional Arguer: "(roll eyes)" (which is a nonverbal insult, mixed with contempt)
That dismissive response is an empty-minded expression, saying that you are not qualified to judge the reliablilty of your sources.
However, some of us can. Some of us. On the other hand, I don't think that people whose form of expression is funny gestures are probably thinking things through.
Mockery is about as dumb as dumb gets.