Well, here's the poem. Let's find out:
Don't be polite.
Pick it up with your fingers and lick the juice that
may run down your chin.
It is ready and ripe now, whenever you are.
You do not need a knife or fork or spoon
or plate or napkin or tablecloth.
For there is no core
to throw away.
First of all, the whole poem is a metaphor - and not a serious or ominous one. A poem is imagined to be like a fruit which can be eaten. And it starts with an instruction that might be a clue to its tone and mood: 'Don't be polite'.
Merriam (the poet) doesn't want us to think of poetry as something refined, cultured, and polite - she wants to plunge in. There is a tremendous vivaciousness and energy about this idea. We have to 'Bite in' to the poem - metaphorically, to really get our teeth into it. So the tone is encouraging, iconoclastic (a word meaning to really reject traditions and find new ways), youthful, energetic and humorous.
To eat a poem, there is no need for a knife or fork or spoon or tablecloth - or any of the things which make eating more civilised. We are being allowed to eat with our hands: bad manners though it may be thought! There is something very open and permissive about the mood of the poem and its message that poetry is for everyone.
There's also a tremendous energy to that final list of things that are wasted when you eat a fruit:
....there is no core
A fruit has waste products that we cannot eat; on the contrary, every single bit of a poem is juicy and edible. It's another thought that throws its arms open to poetry and to any reader - "It's all great stuff!" Merriam is saying, "Devour it! Throw nothing away!"
So, in conclusion - the tone of the poem is humorous, but with a serious purpose and a genuine passion and energy in delivering its key message: that poetry is not something polite, refined and wholly civilised, but messy, human, and open to everyone.