When can I say "who cares"? Could you show me more situation I can use this expression?

Native speaker’s answer
Rebecca
This is an informal expression used to express that something is unimportant or not worthy of being cared about. The speaker has used “who cares” to show that he does not care about the situation, and wants Margo to leave her date. Ex: A: It’s raining out. B: Who cares? I have an umbrella. Ex: Who cares? It’s not a serious injury. I’ll be fine by tomorrow.