Mojtaba bemiri, rahbari-ro nagiri!(roughly; 'die Mojataba, so you won't become the leader').
As reported, "During the past week, rumors have surfaced that [Mojtaba Khamenei, supreme leader's son] has taken over the pro-government Basij militia and that his father is grooming him to be the next supreme leader. Thursday marked the first time protesters chanted against him."
Khamenei's son takes control of Iran's anti-protest militia (Julian Borger/Gurdian; July 8, 2009)