Do I have to feel guilty or is it 100% his own fault?

My twin brother asked me for a very dumb thing recently...he asked me to kick him in the nuts really hard cause he wanted to know how it feels (yes, he's really stupid) and I did...and well, it hurt him a lot and he was down on the ground holding his groin for ages. But my question is, do I have to feel guilty or is it 100% his own fault?
Do I have to feel guilty or is it 100% his own fault?
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