A vindicta is when one djinn declares a blood grudge against another djinn. Within the djinn honor code, all the other members and relatives within the djinn tribes must then go after the declared djinn, often to the death. Because it is an official and recognized event, it is legal under The Baghdad Rules.
Although John Gaunt had the opportunity to declare a vindicta against Izaak Balayaga for kidnapping his sister, he chose not to because he felt pity for the man. The only known sancutary for protection against a vindicta is the House of Kafur.