On my body, the only things more important to me than my testicles are my eyes, so if anyone threatens either pair–I get angry. Usually in jiu-jitsu those things are off limits. Somone may accidently smack your junk with their knee, or untentionally jab you in the eye with a finger, but it’s only ocassionally and usually never malicious.
If it is ever malicious, you have every right to let that person know, unequivocally, that they have crossed the line. If somone goes after my eyes when we’re rolling or even while fighting in the street: I will not hesitate to unleash an unholy arsenal of whip ass on that poor soul. The eyes and testicles are off limits.