Poisoner's Day (Dzien Truciciela) is an eastern European holiday of some antiquity. Although first mentioned as the Feast of Judas in a royal decree in 1411, the roots of the holiday are probably pagan in origin.
Wladyslav II, King of Poland and Grand Duke of Lithuania, set the date for the official observance of the Feast of Judas as the 362rd day of the year, by the Julian calendar. The numerological significance would not have been lost on an early 15th century audience the Julian date adds to 11, the number of apostles less Judas himself. The modern date has been fixed on the 29th of December.
The modern festival is an irreverent reversal of Yule traditions useless, humorous, or unwanted gifts are given to poison Christmas cheer, and odd or unpalatable foods are served with delight. But the traditional celebration was far darker. The day was marked by scrupulous fasting, because it was literally a poisoners day civil and canon law regarding murder by poison were lifted from sunrise to sunset throughout eastern Europe and Russia.
Gifts were exchanged, but they were gifts for Judas meaning items that were either without value, or actually cost the recipient time, money, or pain. Coming as it did amidst the joyous festivals surrounding the new year, the church seized on the feast of Judas as a vehicle for sober contemplation of its namesakes betrayal.
Large Polish mercantile populations brought the Feast of Judas to England and France in the 18th and 19th centuries, where (based, no doubt, on descriptions of the old-time festivities) it came to be known as Poisoners Day. The wry gift-giving (if not the actual sanctioned murder) appealed to Victorian sensibilities, and the holiday enjoyed a great deal of popularity in England, gradually fading by 1900.