What does Boxing Day have to do with boxing?
early 15c., originally in reference to medicine that reduces swelling or humors, from Middle French impulsif or directly from Medieval Latin impulsivus, from Latin impuls-, past participle stem of impellere (see impel). Of persons, "rash, characterized by impulses," from 1847.
impulsive im·pul·sive (ĭm-pŭl'sĭv)
Inclined or tending to act on impulse rather than thought.
Motivated by or resulting from impulse.