Wouldn’t you rather wipe my — for me?

"If you coulda...you woulda..."

This line comes back to me any time I am experiencing a particularly unpleasant bowel movement. Because, yes, I wish there was some asshole out there who could just wipe my ass for me. But then again, of course I wouldn’t actually want that, because my asshole is my business, and I am not nearly as entitled as mr. Costello.
So basically it’s just an insult based in anger and frustration at constantly being hounded by people Costello sees as ‘beneath’ him. Pun somewhat intended.