I understand the expression to mean doing something on a holiday that you would normally do at your job. So, am I to understand that the expression simply refers to a bus driver going for a ride on the bus on his day off?
Various dictionaries confirm this as the meaning and give the first use as 1893: Wordorigins.org points to it in English Illustrated Magazine.
protected by RegDwigнt♦ Nov 18 '12 at 5:07
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