Can be used as an insult/come-back. Originated as a sexual act when a woman (or man) is fellating a man and uses her (or his) bangs to sweep across and tickle the balls.
The term/act was introduced on a women's website called Makeup Alley and spread like wildfire when many of the women tried this act with their romantic partners and reported back to the message boards.
When someone is cranking on you and fucking with you to the point that it isn't any different than having a pitched baseball hitting your nuts or like your balls being put into a vice.
My boss has been grinding my balls all day long about getting that report done.