The Collaborative International Dictionary of English v.0.48:

Larrikin \Lar"ri*kin\, n. [Cf. E. dial. larrikin a mischievous
   or frolicsome youth, larrick lively, careless, larack to
   frolic, to romp.]
   A rowdy street loafer; a rowdyish or noisy ill-bred fellow; a
   hoodlum; -- variously applied, as to a street blackguard, a
   street Arab, a youth given to horse-play, etc. [Australia &
   Eng.] -- a. Rowdy; rough; disorderly. [Australia & Eng.]

         Mobs of unruly larrikins.                --Sydney Daily
                                                  Telegraph.

   Note: Larrikin is often popularly explained by the following
         anecdote (which is without foundation): An Irish
         policeman at Melbourne, on bringing a notorious rough
         into court, was asked by the magistrate what the
         prisoner had been doing, and replied, "He was
         a-larrikin' [i. e., a-larking] about the streets."
         [Webster 1913 Suppl.]