1. I've stepped on legos, they don't hurt 2. The worst pain I've experienced is when i slipped and hit my side full force on a bar thing. And it hurt more than being hit in my testicles.
There is a pain scale, but since there are so many factors affecting the amount of pain felt, it is sadly inaccurate. Here is a video explaining for AsapScience :P
(Childbirth vs. Getting Kicked in the Balls)
(Childbirth vs. Getting Kicked in the Balls)