The Collaborative International Dictionary of English v.0.48:

man in the street \man in the street\ n.
   An average person; as, the views of the man in the street.
   [WordNet 1.5]

WordNet (r) 3.0 (2006):

man in the street
    n 1: a hypothetical average man [syn: John Doe, Joe Blow,
         Joe Bloggs, man in the street]

Moby Thesaurus II by Grady Ward, 1.0:

79 Moby Thesaurus words for "man in the street":
   Cockney, Everyman, John Doe, John Smith, Public, a nobody,
   a nothing, average, average man, body politic, bourgeois, cipher,
   citizenry, common man, common run, commoner, commonwealth,
   community, community at large, dummy, estate, everybody, everyman,
   everyone, everywoman, figurehead, folk, folks, general public,
   generality, gentry, girl next door, homme moyen sensuel,
   insignificancy, jackstraw, lightweight, little fellow, little guy,
   little man, man of straw, mediocrity, men, nation, nationality,
   nebbish, nobody one knows, nonentity, obscurity, ordinary Joe,
   ordinary run, people, people in general, persons, pip-squeak, pleb,
   plebeian, polity, populace, population, proletarian, public, punk,
   roturier, ruck, run, runt, scrub, shrimp, small fry, small potato,
   small potatoes, society, squirt, squit, state, whiffet,
   whippersnapper, world, you and me