What does Boxing Day have to do with boxing?
1690s, Scottish, "aggressive, boisterous," probably from rand "to rave," an obsolete variant of rant (v.). In the original sense especially of beggars, "and probably implying vagrant habits as well as rude behavior" [OED]. Sense of "lewd, lustful" first recorded 1847. Related: Randiness.
[1847+; origin unknown; various dialect senses suggest a possible derivation fr ''wild movement,'' ''boisterousness,'' ''wantonness'']