When I was a boy, my mother usually disciplined me with the hairbrush. If my dad was called upon to discipline me, it almost always meant a trip to his workshop for an appointment with a stiff hickory switch, his carpenter's ruler/straight-edge, or his razor strop.
When my sisters and I got into trouble together, we were usually punished together. When I hit puberty, this became embarrassing and I would get erections. My dad said that this was normal for boys in puberty, but my sisters would tease me.
When I was 12 and my older sister was 16, my parents left her in charge for a weekend, while they were out of town. My younger sister and I thought this meant we could get away with anything, but when my older sister finally got fed up, she told me to fetch the hairbrush. We protested, but she said that we needed to obey or dad would tan our hides with the strop when he got home.
So, I fetched the hairbrush. After we had stripped, my younger sister went over my older sister's lap first. By the time her paddling was over, I was standing to the side with a rock hard erection. Being taken over my older sister's lap, with an erection, was more embarrassing than almost any other spanking I'd ever recieved. After about 5 swats, I experienced sexual convulsions and had an explosive orgasm. My sister just ignored it and kept me restrained over her lap while she finished paddling my bottom. I was totally flaccid by the time she was done spanking me.
Thus, my fascination with the hairbrush.