Shall I part my hair behind? Do I dare to eat a peach? I shall wear white flannel trousers, and walk upon the beach.
As one of the annotated guides to Eliot’s poems put it, parting your hair behind was considered "daringly bohemian" at the time.
Prufrock is still trying to make all kinds of tiny decisions, now that he has missed his big chance. As always, he’s interested in the small pleasures of food and fashion, like the peach and the white flannel trousers.
He’s also going to check out the ocean – maybe he’ll talk about how he wants to be a crab again.
I have heard the mermaids singing, each to each.
OK, so no crabs. Instead, he sees some mermaids.
Wait, that’s actually pretty exciting. But this is Prufrock, who can’t keep track of what time it is, so he says he has "heard" the mermaids singing to each other, as if this event were already in the past.