whether or not you are going to donate it should not depend on the condition of the instrument. It is your piano, you payed for it, and you can do whatever you want with it without feeling obligated to help anyone.
If I knew a millionaire who didn't want to give any of his money to charity, I wouldnt pass judgement; it's his money. of course, it would still be a kind gesture (unless he's just doing it for reputation) to do so.
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that said, I think a fun way to destroy it is to put pins in the hammers and make cool sounds until the strings snap
after that, take the keys out and make a piece of art with em
take the soundboard out, hang it up and turn it into a gong
*EDIT: just saw this:
Looking for a quick and effective way.
yeah, my vote goes for the ax. do it for firewood, as nicco said and throw the metal parts out on the lawn like a redneck
