Here are some expressions to convey that meaning:
"Non importa", it is polite. (it is like "it is not important", "it is not necessary")
If you say "non me ne importa" you somewhat emphasize the meaning and the sentence becomes a little bit rude. I think it is like "I don't care" in English.
"non me ne importa un accidente" in even ruder
But the rudest ones are "non me ne frega nulla/niente/un accidente" or "non me ne può fregare di meno" which is like "I don't give a damn", finally you can also say "non me ne frega un cazzo" (I don't give a fuck). Cazzo is a curse word in Italian.
I apologize if someone finds this disturbing but after all curse words are part of languages.
I bet I remember this without even trying!