It's pretty much impossible to walk from the office to the shops where I buy lunch without going past, and being accosted by at least one person soliciting for a charity. I find this sort of thing really intrusive. I understand that it's probably a very effective way to get people to sign up (they generally ask for ongoing donations, they're not just holding up a bucket), but it's still an invasion of my personal space, and a disruption of my train of thought.
What's worst is when I get accosted by one of the charities I am already a regular donator to. It makes me want to ask them to take my name off their list so I can give my money to someone less annoying.
I would love to, next time I am cornered, just say “Why? The world's overpopulated as it is”, or ”Why should I care about Pandas? They can't even screw to save their own species.”
I wouldn't, of course. But the thought is enough to get me to my lunch without growling at some poor volunteer who is doing a really worthy, but incredibly annoying job.