nonchalant
adj.adj. relaxed and calm, showing that you are not worried or do not care about something.
adj. displaying a calm, relaxed, and unconcerned manner. Often implies a deliberate lack of enthusiasm or anxiety in a situation where such emotions might be expected.
He gave a nonchalant shrug when I asked about the missing money.
Despite the intense pressure of the final exam, she remained completely nonchalant and finished her paper early.
His nonchalant attitude toward the company's declining revenue frustrated the board members, who expected a far more urgent and proactive response from their chief executive.
Borrowed from French nonchalant, from Old French nonchaloir (“to be unconcerned”), from non- (“not”) + chaloir (“to have concern for”), from Latin non (“not”) + calēre (“to be warm”).
Typically followed by the preposition 'about' when specifying the object of indifference.