The text plays on the cultural and linguistic differences indicated by the phrases 'y'all' and 'youse guys', which are colloquialisms respectively associated with the Southern and Northern United States. The Mason-Dixon Line historically demarcates the boundary between these regions. The humor arises from the regional dialects rather than a play on the different meanings of a single word or similar-sounding words.
Mason - Dixon Line n . Separates y ' all from youse guys