Even though Jax has bouts of rash, impetuous behavior, he normally has an unexpectedly calm and composed demeanor. Yet, his flattery is generally insincere and often insulting. It is possible that he does care for his friends and that his insensitive nature is  merely a front. 
Evil Jax is ironically the exact opposite of the original Jax; he is meek, shy, and exceptionally kind to others including his evil teammates. His harmless and overly polite nature help the sanest characters feel at ease.