system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why is testicle pain more painful than pain in say the arm or leg?
gpt
There are two good answers here, but the full picture needs to put both of them together. 

Get yourself two toothpicks. On yourself without looking or on someone else without them looking, test to see how far apart they have to be for you to realise it is two toothpicks and not one when you press them against the skin of your fingertips. Try this again with the skin of your upper arm/thigh etc. 

Different parts of your body are better or worse at detecting touch depending on the density of touch neurons, and subsequently a smaller or larger portion of your brain is devoted to processing those signals.

Pain receptors are different from touch receptors but the principle is the same. More pain receptors in an area will mean that you will be able to feel more pain in that area. Hence why there are more pain receptors in places that you need to survive and procreate.

 There is strong evolutionary pressure to have lots of pain receptors on your testicles, as trauma to them will screw up your chances of having kids. Therefore, making trauma to your testicles unpleasant makes you more likely to protect them, and makes your genes more likely to survive.