There are a few etiquette rules that have to be followed in a public setting and using left hand for doing few things is one of them. While many people may overlook them but we tell you where you shouldn't.
When passing dishes to your right during a formal dinner.
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When holding your iPhone a you get better reception from the right.
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When communicating through sign language, don't switch your dominant hand and stick to one side.
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When passing things to people in India.
While eating food. Use only one hand at a time.
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While touching money in the Middle East.
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Writing in Japanese, you will be going against the stroke if you write from right to left.
