Yesterday, on my way to the Metro from work, I came upon a street corner where two people (presumably college students) in Greenpeace shirts were making their pitch and asking for donations and such. When one of them addressed me, I said that I had donated to Greenpeace online and signed some of their petitions, both of which are true.
He asked me if I was a monthly donor, and I said no, I wasn't. He then basically said that supporting the organization online was not enough. "You know grassroots activism is important, right? You can't do real grassroots online." I'm paraphrasing a bit here, but that is basically what he said.
I got rather peeved at this, and told him "I don't like being charity mugged." While he was being incredulous and obviously not getting the hint that he'd totally lost me, I crossed the street.
Maybe I was rude and maybe that guy now thinks I skin panda bears in my spare time or something. But when I say that I have already given some support to the organization you're pitching for, the appropriate thing to do is to say "thank you," and politely ask me if I would consider becoming a regular donor. Maybe tell me about some initiatives you're raising funds for, and see if I'm interested in them. Scolding me for not demonstrating an appropriate level of commitment to your organization is a real turn-off.
My mother says that in these situations she uses the line, "I have a list of charities I donate money to, and you aren't on it. Sorry." My grandpa says - or claims he says - the following. "Look, my parents are very sick and have high medical costs. My brother just lost his job and has four kids to support, and my neighbors across the street had a fire in their house and are broke after fixing it up. I don't help any of them, why should I help you?"
While we're on the subject, what is your preferred method for dealing with charity muggers?