These two words could be the most irritating words spoken by your teen. They refuse to do what you ask of them, or they flout some rule that you thought had been agreed upon, or the report card comes in the mail with less than stellar grades even though they had sworn up and down they had pulled their grades up. You give then a consequence that you hope will mean something and teach them a lesson, so that the next time XYZ happens they will think first of the consequence that will be meted out, and not do the wrong thing. You hope and expect to hear anger and moans and groans. That at least means that you have "gotten" to them, and perhaps have taught them a lesson. But when you hear the "So what, who cares?" your well-laid plan goes off course. Your buttons get pushed, and off you go to the land of "argumentamia." Your teen has played the game well, and seemingly taken away all your power.
It may be that your teen responds in that way, because they know you, and know that the consequences you put into play are often forgotten about or reversed easily if a good argument can be made. Or perhaps they are just trying to goad you into a bigger argument, knowing how best to push your buttons. Or perhaps they really just don't care. I had a mom recently tell me of a situation with her 12 year old son whose attitude was out of control. At her wits end, she took away his X-box, expecting an instant apology and promises to change. It turns out he coulda cared less. "Fine, take it away...I don't care!" And I guess he didn't much care, cause he still hasn't asked for it back.
Remember that when you give a consequence, expecting that the consequence alone will change the behavior, is unrealistic. If it is a kid with an attitude, you have to show him what you need him to do differently. If you take away your teen's cellphone when he has an attitude towards you, and expect that he will not have an attitude with you again because he/she is worried they will lose their cellphone, you will be disappointed. Just saying..."change your attitude, and if you don't, I'll take your .....away!" will not change an attitude. When teens are in their emotional place, in the moment of frustration and anger, they can't and don't stop and think: "Oh I better tone it down if I don't want to lose my phone again." Perhaps you need to model the kind of behavior you are looking for. Maybe say: "Want to try saying that a different way, so I can hear it?' said calmly and in control! If your teen chooses the "I don't care, do what you want" thing, rather than get mad, throw out a coy smile, a shrug of the shoulders, and you are back in control.