Onscreen king of kvetch Larry David just couldn't contain himself at a Martha's Vineyard parking lot last weekend when an errant shopping cart scratched his beloved BMW 530. According to Page Six, the "Curb Your Enthusiasm" and "Seinfeld" creator and his wife were outside a Vineyard Haven supermarket when a runaway cart made what one eyewitness said was "a little dent" in David's $75,000 car. David proceeded to call the cops and started, says the witness, "in a golf shirt and shorts, flapping away with his arms. It was just like an episode on his show." Vineyard cops confimed that...