Massacree

"Massacree" as used by Arlo Guthrie is a series of absurd events. He calls his movement in the song the "Anti-Massacree Movement" because he is protesting the crazy situations in the world that lead to the song.

And can you imagine fifty people a day? I said FIFTY people a day
Walking in, singing a bar of "Alice's Restaurant" and walkin' out? Friends
They may think it's a Movement, and that's what it is the Alices's
Restaurant anti-massacree movement. And all you gotta do to join is to
Sing it the next time it comes around on the guitar