Feed The Birds are a UK based anti prohibition activist group. They believe that by spreading hemp seeds in public places, any seeds that don't get eaten by the birds will grow into a plant capable of making a mockery of the unjust, hypocritical and absurd UK drug laws.
Dad: Okay son, do you know what the birds and the bees are?
Son: It's when a guy and a girl-
Dad: NO! IT IS A METAPHOR! ONLY A METAPHOR!
Son: A metaphor for what
Dad: A METAPHOR FOR METAPHORS!
A phrase commonly used to signify that one will not get any left over food. The meaning is that instead of giving leftover food to the person asking for it, you would rather scrape it outside for the birds to eat.