dictionary.com definition of rude said:
discourteous or impolite, especially in a deliberate way: a rude reply.
So I'm not alone in thinking rude is an antonym of courteous. Courtesy is more than tone of voice, or if you want to argue that it is only tone of voice, then it is not rude to accuse someone of cheating with a friendly voice (well, at least according to dictionary.com).

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