Just that really.
Admiration and gratitude have to come genuinely. A guy does an amazing sponsored walk. you feel admiration and gratitude- that day. The next day you move on... but no, you can't, he's become a sort of BBC-sponsored saint. It goes on the next day … and the next day.... and then he's a sort of Ghandi figure … and there's a godawful record.....
And as for Over the Rainbow on the street it's very simple. are you Judy Garland? Are you Eva Cassidy? Are you exceptionally skilful and able to perform quietly so those neighbours who don't want to hear you are left in peace? Unless you can answer yes to at least one of those questions, I am going to throw a bucket of water over you and I am not going to be sorry.