Or you could say something along the lines of:
Look, mum, dad, its not that I don't appreciate everything that you have done for me, It's just that I'm dissapointed in your lack of support over these last few years. If you had took the time away from your own interests for a while, you would have recognised that I was struggling in certain areas of my life.If you had paid attention to my needs a little more, we wouldnt be having this conversation now, hopefuly you will grow into the understanding parents that i should have come to expect, and you could start by giving me some encouragment on making some more of my life with these grades *hand the report over*