That right there is a move which will alter this friendship for the rest of eternity. There's simply no returning to a point of normalcy after a nut shot like that. And don't get me wrong--cup checks are always funny. Always have been and always will be, barring you're not the one whose balls end up in their chest cavity afterwards. But there's a difference between a cup check for the boys, and getting your nuts Hulk punched into Bolivian.
That was as direct a shot as they come. He stepped in and let that one rip. This son of a bitch may not have ever been in an actual fight his entire life but somehow he managed to channel the force of Tyson there. Live look at my man's sack after that underhand bazooka blast.
In an actual fight you're taught to always keep your hands up. But when you're boxing against one of your boys, you should ALWAYS keep at least one of your hands down because your buddies aren't going to be trying to send you to sleep for the next week. Your buddies will just be looking to absolutely smoke you in the nuts because it's going to be hilarious for everybody else. So as much as this might have been over the line, you still have to victim shame a little here since this poor bastard didn't even anticipate the possibility of getting an impromptu vasectomy that day.
Sidenote: Locker Boxing is one of the greatest traditions in all of sports.