Another story from a client:
It was winter. I was 13. My friends, all a bit older than me, challenged me to shinny up a flagpole. No problem. I went up maybe 20 feet. They were impressed.
Then I slid down. The crotch of my pants was in contact with the cold and somewhat rough pole surface. I felt the vibration of sliding down in my dick, and suddenly felt something really strange that weakened my knees.
I told them I felt a ‘sort of pumping feeling.’ They all laughed. I had no idea why at the time.