Bonta's tiny poem is a joke with a slightly serious edge. Its speaker says that the "dinner self," the version of us that sits down to eat, doesn't care about "dinner manner." Good etiquette, in other words, matters less to the part of us doing the eating than it does to everyone watching.
The second stanza turns inward. Even when alone at supper, the speaker finds their own company more entertaining than any "unparliament." That odd, invented word seems to mean a chaotic gathering of voices, perhaps a noisy table of people talking over one another. The speaker would rather sit with their own thoughts than put up with that.
The mood is dry, playful, and a little contrary. The speaker sounds comfortable and self-contained, maybe slightly smug, and the wordplay (the near-rhyme of "dinner" and "manner," the made-up word) makes the whole thing feel like a quick, wry aside rather than a lecture.