1. when something happens that leaves u with absolutely nutin to do but for your two nuts to (imaginatively) knock against each other
2. bangin' balls - the act of above
3. bang balls also means a fuck-up. for example when something happens not in your favour, or something embarassing happens to u, u can say "bang balls man!"
usage 1 - "yo bitch left me bangin balls, she ditched me midway and hit d clubs downtown! puta!"
usage 2 - "shit, the whole bar was watchin me drink d flaming, and i had to fry my fuckin eyebrows man!"
"Shiiit man, really?! haha! dats a major bang balls, bitch!"