Throughout the play you will notice that there are many oaths that begin with "Od" or Odd's" and this is a euphanism for "God" ;-)

The "foot on the bar" comment is quite clever:if we lookat his whole speech:

More’s the pity! more’s the pity! I say.—Odd’s life! when I heard how the lawyers and doctors had took to their own hair, I thought how ’twould go next:—odd rabbit it! when the fashion had got foot on the bar, I guessed ’twould mount to the box!—but ’tis all out of character, believe me, Mr. Fag: and look’ee, I’ll never gi’ up mine—the lawyers and doctors may do as they will.