Oh, It's An Irish-Catholic Thing

This 'one'.  That 'one'.  Another 'one'.  Chris Matthews says that it is an old Irish-Catholic thing.  And I am inclined to agree.  John McCain was born an Episcopalian Scots-Irish American.  But he would be old enough to have picked-up on this use of the word "one."

School teacher:  "You're a smart one."

Grandma (let's call her Rose):  "Which one of you little devils broke my coffee mug?  That one!"

John McCain:

And Mocean Worker quickly produced this great little diddy (H/T to Driftglass for finding this):