I'm 16. (Yes, that's right KH13, you know my true age now! It's no longer the Blossom mystery)
I do live under my father's roof, but in this situation I wouldnt be using any of their money, I would be using my own from selling something of mine I didnt want anymore. If they made the argument that they bought that item for me, I would just sell something a friend gave to me if it was alright with that friend. But I agree though, it's my money, I should spend it how I want to. Plus, it's not like Im blowing 300 dollars on alcohol or drugs like some teens, or spending it all on designer clothes, or some selfish or irresponsable indulgence.
I just want to donate 1-5 dollars to charity.