The six inch rule is a commonly accepted rule of etiquette, even if it's not official. The idea behind the six inch rule is personal space. One is to be allowed and given six inches of air between them and anyone else in order to avoid uncomfortable contact or awkwardness due to close proximity or the appearance of being cold with too much distance.
John remained respectful of Mary's six inches of personal space, and he was later rewarded for his consideration and careful adherence to the six inch rule.
Dude, it's the six inch rule, so get the fuck out of my face.
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