Meaning of "Git 'R Done"

For that matter, how is Larry the Cable Guy associated with comedy?

I saw a SUV the other day that obviously had been decorated for a wedding. On the back someone wrote in white shoe polish “Git R Done”. Had I been the bride I would have refused to set foot in that car.

Somehow, this insipid phrase and the relentless marketing of it reminds me of the “I’d buy that for a dollar!” tag-line from Robo-Cop