When I was a boy, up through age 17 even, I'd challenge anybody
  who challenged me: " Go ahead: Knock me down ". From probably
  2nd grade through 11th grade, although by 11th grade, I was
  doing the challenging just for fun, but before then, they had to
  initiate some sort of bullying affair with me. Try as they
  might, nobody ever did.* I knew how to stand and nothing would
  move me. Until 11th grade.* I was cocky.* "Go ahead: Knock me
  down!" I said for one last time.* A boy smaller than me pushed,
  and I found myself tumbling over: His friend had knelt behind my
  knees, exposing my one weakness.** [I'd grit my teeth through
  smartasses who would kick me in the groin in younger years,
  although that was quite rare; happened perhaps twice]. Anyway,
  after that back-attack, I knew my days of physical battle were
  over.* There was now so such thing as an honest fight, so why
  engage in the first place?