I used to swim nude in my boy's junior high school swim class. Our gym teachers always made us start out the classes with exercises on the pool deck the first one being 100 jumping jacks. After about 10 jumping jacks my penis would become erect and for the next several minutes I would be there with my 7 inch bone slapping up and down, up and down, up and down. It would usually stay semi erect for most of the gym class. Push ups, sit ups and then swimming. Did any else have this same experience? The gym teachers got a great kick watching about 30 boys bare ass going through the routine.