And it's not a day where you celebrate everyone called Hilary, either. No, Hilarymas is a Swedish event on January 13 in which trees can literally fly out the window. (My advice: Practice defensive walking, and duck when needed.) Hilarymas also marks the end of the Swedish Christmas season with get-togethers, lots of food, dancing, and plundering the tree of edible decorations. The day is also known as St Knut's Day.