I am not a native speaker of Japanese, but it seems to me that there are more (and maybe more useful) expressions than the ones mentioned above. For example: 興味ない（きょうみない）No interest 関係ない　(関係ない) literally "no relation, no connection", often used in TV dramas where one person means "none of your business!" or "So what?!" まぁ、いいか　（sometimes まぁ、いいや！）"oh well, never mind."-----when someone previously was concerned about something, and then decides it doesn't matter そんなのしらない　"who cares about that?!"------ depending on context either sounds kind of dumb (don't ask me about brain surgery) or very dismissive and rude (your dying grandmother is not my concern) もういい！　　"enough already!" (can be used in ending a relationship when the speaker feels disrespected) No doubt some native speakers can think of numerous similar expressions and expand this list.

well, as for かまうものか　sounds actually really old to me. it's like, as if an ancient warrior said that or Samurai said. but i don't know, some old people still might use it. i've heard it in some particular historical TV drama, like Samurai stuff. but i'm pretty sure young people wouldn't say that nowadays. well, but i don't know, i can't say all young people, because some people who want to try to be Samurai or an uniqui person, they might want to use it ;) as for " I don't care" in the apathetic way, i would say 　別に気にしない、どうでもいい、別にいいよ　etc. it depends on situations, so it changes what situation you are in :) hope i was able to help you with this quiestion :) good luck :D

かまうものか is a defiant expression. An apathetic expression equivalent to "I don't care" is どうでもいい

ok