We can rule out Bell, Cook, Swann, Broad, Finn and Anderson for the same reason Peter Costello will never get testicular cancer or Barnaby Joyce a brain tumour.
Joe Root, despite his name, hasn't had his balls drop yet, same with Compton. Pietersen is returning from injury and might be reluctant to risk groin trouble. Same for Bresnan, while Prior wears gloves on the field which makes it unlikely to be him. Onions unlikely to get a game, and the thought of scratching your balls with onion hands is not a pleasant one to begin with.
For mine it's likely to be Trott. He has the experience now to properly express himself, and it isn't like he has any other way to entertain us.