I kinda regard that phrase as a chastisement.
"You're Flogging a dead horse" I mean your attacking the action, but your also saying to the person your wasting your time.
If someone is deathriding, your probably chastising them.. Which is WAY too bigger a word here. I mean what the hell are we english teachers or something.
"Mate, Quit it!" does the trick Jimmy Bob. Or goa "Leave that dead Sheep alone, it's no longer fun" Works for Benji and our cussi Bro's across the tasman (or the other sea thing, I don't frigging know!)
It's a damn Footy forum. Were NRL fans, we should just use sign language, words are far too fancy for us.