"Have you ever seen a bear on acid?
No, But i've seen a Care Bear on acid...
So I guess...exacccctly....a Chugger"
One effective way of giving to the charity, yet not being conned into surrendering your card details and other sensitive information is to request the address and contact details of the charities head office and offer to make a direct payment. This will annoy the chugger as it cuts them out of the equation but you will have the upper hand. Otherwise try to think of a quirky reply to their begging for which they will have no answer or look straight through them.
Me: Yes, but I couldn't eat a whole one.
Chugger: (silence and look of shock)