And I have known the eyes already, known them all— The eyes that fix you in a formulated phrase,
Here he goes with the body parts again – this time it’s "the eyes." The guy has seen a lot of eyes in his time. (Are we supposed to be impressed?)
He’s trying to cover up his fear but not doing a very good job.
He doesn’t like how eyes seem to "fix" or freeze him, and a "formulated phrase" means a phrase that judges, summarizes, and reduces something complicated to something simple. We don’t know what phrase he has in mind, but it shouldn’t be surprising by now that he’s afraid of judgments of any kind by other people.
And when I am formulated, sprawling on a pin, When I am pinned and wriggling on the wall, Then how should I begin To spit out all the butt-ends of my days and ways? And how should I presume?
Oh my. Now he’s really starting to lose it. He’s starting to confuse his verb tenses. He just told us that he has "already" known the eyes that would formulate him, but now he talks as if this event hasn’t happened yet. Which is it, Prufrock?
We’re starting to think he hasn’t really "known" anything at all.
He imagines himself "sprawling on a pin" and put, "wriggling," on a wall.
He’s referring to the practice, in his time, where insects that were collected by scientists were "pinned" inside a glass frame and hung on a wall so they could be preserved and inspected. If you go to a really old science museum, you can sometimes see examples of these insect specimens.
So Prufrock is imagining that the eyes are treating him like a scientist treats an object of study. He doesn’t like that so much.
The image of a guy tied down and "wriggling" might also remind you of the very first lines of the poem, when the evening was "spread out" like a patient on the operating table.
Prufrock seems pretty spooked by doctors and scientists – maybe because these people can see things for what they really are.
He thinks that once these scientific eyes have got a hold on him, he’ll have to talk about or rather "spit out" the story of his life ("days and ways").
The "butt-ends" could refer to any kind of end – the little odds and ends of his daily life, the evenings he spent, etc. But it’s also the word people use for the end of a cigarette, the part that doesn’t get smoked. Prufrock is comparing his life to a used-up cigarette.
Oh, and, by the way, he’s still worried about "presuming" too much about the situation. Thanks for the reminder, Mr. P.