Jack appears to be very headstrong and reckless, having decided to attack four Marine ships at once, which were carrying powerful Marines, to rescue Doflamingo.[1] He has shown to be extremely impatient, growing angry when one doesn't comply with his orders immediately. His rejecting of Inuarashi's offer shows that he also refuses to compromise with others.
He is also rather sadistic, not being above torturing enemies in order to get what he wants. Jack has been shown to be horrendously violent, fearsome, and short-tempered, as one of his subordinates worried how Jack would react once he learned about Caesar Clown's downfall. He threatened to destroy an entire city should he not get what he wanted, and made good on his word. His ruthlessness extends to even attacking elderly and children. He has even admitted that he has a love for causing destruction. Some people who have met him even describe these traits as insanity. [5]
He is shown to be stubborn and unreasonable not unlike his superior Kaido, as seen when the minks tried to tell him that Raizo wasn't on Zou, but he refused to listen or believe them and even bluntly told Inuarashi 'No' when the latter offered to let him search the island without any resistance to see for himself. This, along with him disregarding his crew's comment that attacking Doflamingo's convoy was dangerous, shows that he refuses to listen to logic. He takes his unreasonablility to a point that he actually becomes enraged when someone even tries to reason with him. Also, he is not above fighting dirty as he brought in Caesar Clown's gas weapon to annihilate Zou after the minks put up a formidable fight against his forces