You know how practically every male human in any human-in-equestria story is kicked in the nether regions by Applejack? That should pretty much be the very end of the story according to logic.

A horse's kick can exceed two thousand pounds per square inch of pressure. Assuming any grown pony's kick has at least a fourth of that, that means they can give a kick of over 500 psi. Since Applejack's hereditary traits and lifestyle, one can assume that she has a lot more power than normal ponies, especially when it comes to bucking.

A human testicle typically can resist anywhere between 110 lbs and 200 lbs of pressure. The average size of one is around 18 square inches. That means they rupture somewhere between a range between 3.05 and 5.55 PSI.

That means that even a frightened kick from Fluttershy of all ponies would be almost 100 times more force than needed to break ones balls.  One would probably go into shock from the sheer amount of pain they are experiencing, and if that didn't do them in, you also got blood loss and the problem of having medical professionals who do not know what to do in such a situation working on you.

So basically, when they're bucked in the fruit by Applejack, unless they're wearing some heavy duty protection on that part of their body, their balls would probably just explode like a watermelon being shot.

Pleasant dreams everypony.