When a small male (including, but not limited to humans) has an issue with the rest of society because society tends to look down (literally and figuratively) on
small people. Little Guy Syndrome (also:
Little Man Syndrome) gives the "infected" person a aggressive attitude and thinks he some kind of "playground
Muhammad Ali," and can beat everyone up.
NOTE: Not all small male humans, dogs, etc. have Little Guy Syndrome. And oddly enough, legitimate midgits tend not to have Little Guy Syndrome because they've already accepted the fact that they'll be forever short.