Sometimes it's a tactic - they pretend that they misunderstood you in order to guilt-trip you, sidetrack you from your point in a discussion, erode your self-confidence, put you on the defensive - in short, to weaken you. Not in the example of the cab driver, of course. But often when people accuse you of trolling, it's a bullying tactic.
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So-called white lies are like fake jewelry. Adorn yourself with them if you must, but expect to look cheap to a connoisseur.