I just posted about ways to punish assaults on male genitals. But I think equally good results could be had by showing in detail why those assaults are so unacceptable.
I suspect many attackers assume those attacks are merely inflicting pain. Even if we just focus on the pain, they should know that, if a victim lacks previous experience with the extreme pain, he might feel like he has been horribly injured, which adds to the psychological trauma. A groin attack sometimes is more than a regular assault, due to the level of pain intended and the risk of permanent injury: depending on the guy and nature of the hit, it can be closer to torture than to a hit to other body parts.
But there is more than pain involved. For one thing, links to pages like
http://www.mens-rights.net/law/violence/testicular_abuse.htm explain that there are lasting health and fertility consequences.
It also helps to focus on the reasons given for the assaults. Searching on Google for something like "why girls kick balls" yields various answers.
One answer is that some girls mistakenly believe that all guys believe they are tough and girls are weak (and the girls want to punish/counter this imagined arrogance). Why do girls keep saying that? Many guys don't think that. Those guys that do think so, don't necessarily think they are invincible. I suppose many cultures or individuals do exaggerate male toughness and female weakness, but girls are not entitled to disprove it by hitting testicles.
And there are other answers that need to be countered: amusement at the reaction (victims' facial expressions and words), misandry, sadism (laughing at the hurt), ignorance or misunderstanding (thinking the laws of assault and battery don't apply when females hit males), arrogance and entitlement (thinking they may physically punish those whose words they dislike), and seeking a power trip (girls normally are too weak to hurt men, so it's a special opportunity).
As I suggested in my first thread I posted almost half an hour ago, Hollywood's screenwriters are in a unique position to educate on this matter. These ideas haven't been covered much onscreen, so it would be original and interesting, if the writers can figure out how to handle it.
Other than that, I'm not sure how the word should get out.