1. A thoroughly devastating or disappointing setback or failure. Losing the championship match was a real kick in the head, but I knew I just had to train even harder and try again next year.

2. A harsh punishment (or remedy) for acting foolishly or malevolently. Usually used prescriptively (i.e., "(someone) needs a kick in the head"). Tim needs a kick in the head for passing up such a fantastic job opportunity. Whoever has been spreading rumors about Cathy deserves a kick in the head.