1. An attack to mens genitalia (sometimes womens). Sometimes enjoyed sexually, sometimes just outright painful. In the
wrestling world women wrestlers low blow men wrestlers a lot, primarily to help their man win a match, or to excite the ballbusting fetishists like me who watch. Chyna is the most famous female low blower in WWE/F history, but Lita is
getting up there too. I would rather be low blowed by LuFisto than any
other woman wrestler.
2. A comment which is cruel and callous. Meant to cut like a knife. Hence the term low blow, it hurts.