Behaving in a calm manner often in a way that suggests you are not interested or do not care. (Cambridge Dictionary)
If you describe someone as nonchalant, you mean that they appear not to worry or care about things and that they seem very calm. (Collins Dictionary)
(of a person or manner) feeling or appearing casually calm and relaxed; not displaying anxiety, interest, or enthusiasm. (Oxford Dictionaries)
Having an air of easy unconcern or indifference. (Merriam – Webster)
Why are some people nonchalant?
Why are some people indifferent to almost everything?
Why do some people act like they don’t care?
Why is someone nonchalant in everything in his life like he doesn’t care about anything?
How to be nonchalant.