When I was nine years old, I went through a phase of dirtying my underpants, mostly through not wiping my bottom properly after doing a poo, but sometimes through farting or scratching my bum when it itched.
My mother, needless to say, was highly unimpressed with the number of dirty pants in my laundry basket, and one evening her patience finally ran out. She took down my pyjama trousers and gave me a well-smacked bottom with her hand as I stood by her side. It had been some years since I had been spanked, and I cried copiously with both the shock and the soreness of my bottom.