It's in the letters linked to in this thread. The the first one I pulled up actually, about toddlers. Tapping fingers and a "Fanny Whacker".
I had read these when I first joined GCM and saw the links and really enjoyed them, but I did remember the punitive ones . . . I didn't notice nearly as much then because I wasn't as sensitive to it back then I guess. So when I saw this thread I looked for it . I'm going to do some more reading today and find the parts I had enjoyed when I first read them