Always strike more softly than what "feels" reasonable to you. Good rule of thumb: striking our testicles hurts 10 times worse than you think. In middle and high school girls would "sack tap" guys, then one guy's testicle was ruptured and they started enforcing rules seriously.
I still remember my worst ever "sack tap" from a girl in my class. I was curled up on the ground while she laughed with her friends. So I returned the "tap" tenfold in revenge the next day. I knew she didn't have testicles because I had seen my big sister naked. But surely it would hurt when they just have holes there.
I was surprised that her crotch was hard like a bone, not soft like what I had. When she didn't fall down I felt a huge surge of adrenaline. Didn't cover my gonads fast enough though, and she kicked them so hard I was retching. Meanwhile this group of girls is standing over me slapping their pussies and laughing.
