Go away!

Willow: Go away! This is my bench! It is mine by right because it keeps me dry from the drizzle.
Me: Eggy is on the other unsheltered bench at the bottom of the garden getting wet. This is his garden, not yours. Do you think this is fair?
Willow: Yes.
Me: Eggy is old. You should give up your seat for the elderly.
Willow: He's past it. I am the future. Can I sit on your knee?

What can you do?