International Skeptics Day

Takes place 3 times annually, on the 13th of the month of January, on the 13th of the month of October and on the same day as Blame Someone Else Day.

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References:
daysoftheyear.com/days/skeptics-day/
holidayinsights.com/moreholidays/October/internationalskepticsday.htm
checkiday.com/…/international-skeptics-day