śmigus-dyngus

The second day of Bright Week—the Octave of Easter, is a public holiday in Germany, the Netherlands and Scandinavia as an extension of Eastertide and events sometimes traditionally include egg races and other activities to use up, put away the festoonery—a pretty practical idea, which in parts of central Europe, including parts of Poland, Czechia, Slovakia, Hungary and Ukraine they had down to a science, once at least though the practise seems to be less and less common.
Called in Polish above and Oblévačka in Czech, “Wet Monday” (or simply Dyngus Day by diaspora) was chance for adolescents to throw water on each other and flirtatiously beat each other with willow branches that made up traditional egg trees and decorative boughs. With suspected roots in pagan fertility ceremonies and the welcoming of spring countered by Christian missionaries trying impose their religion on the natives, linguists conjecture that śmigus refers to baptism—an involuntary or unwanted one at that, going all the way back to the conversion of Mieszko I, the Duke of the Poles in 966 (coincidentally also on this day)—and Dingnis—from the old German for ransom—refers to the tribute that one can pay in leftover eggs to avoid getting doused or whipped.