He kicked the brush and let a small rock skip doing a dusty dance ahead of him; then finding it before his feet began to toss it with his toe again.
There was a blue jay jawing from above— it made him flush ... a bird might somehow sense the need to play the old game 'kick the can' should be inside of such a "great-big-man".
He kicked the stone into the brush and grumbled, "Clown!" "A great big man" was what the jay threw down.
A grown man is walking alone, idly kicking a small rock along the ground, when a blue jay starts squawking overhead. He takes it personally. In his embarrassment, he imagines the bird has noticed him playing a childish game, "kick the can," and is making fun of such a "great-big-man" for doing it. The name-calling, though, is his own invention: the jay is just a jay, and the mockery comes from inside him.
The poem's charm lies in this small gap between what happens and what he hears. He flushes, grumbles "Clown!" and sends the stone into the brush, as if ending the game could save his dignity. The last two lines hand the jay the final word, which is a nice touch of humor, since it suggests he can't escape his own self-consciousness. The mood is light and gently comic, with a hint of tenderness for a man caught being playful when he thought no one was watching.