Behold, the magic of science:
In the study, reported in the British Journal of Dermatology, healthy male and female volunteers aged 22 to 59 were made to itch by rubbing them with cowhage, a plant with tiny hairs that irritate the skin.
The itches were induced on three parts of the body – forearm, ankle and back. For five minutes participants were banned from scratching, while being asked to record how itchy they felt at each spot.
Then the researchers scratched each location themselves with a laboratory brush, to ensure a consistent technique. The volunteers were asked how pleasurable the sensation was.
Results showed that the itch was felt most intensely at the ankle, and that was also the spot where the pleasure of scratching was felt most keenly and persisted longest.
I think they purposely didn't test a few other spots on the human body: Link