At the risk of being boring (compared to the left hand turn taken by fellow posters) have you tried varying accents or vacabularies?

"Hey Buddy."

"Yes, can I help you"

"yeah. Get yer butt over here."

If you have the characters established, it's real easy for the reader to tell who is who. Actually it's easy to establish the characters this way. Remember the old saw that people judge you by how you dress and speak? This method beats describing a dress!

Just a thought

Chuck S.