The speaker said it himself! His "mind's not right" and it becomes more and more clear as "Skunk Hour" progresses. Because we don't find out this little tidbit until the last half of the poem, it sheds a whole new light on things for your second read, and gives us an explanation for the scattered way the speaker reports what's happening on Nautilus Island. He becomes more disturbed at night – things start to appear more threatening than they are, he's restless, and seems in search of something he never finds. So, there you have it – our speaker, our guide through this poem, is a little off kilter, and we think it makes the ride all the more interesting.
The speaker isn't mentally ill. He's just feeling a little down in the dumps and is tired as he's driving around at night.
The speaker was driven mad by the "you" (implied in the "our" in the final stanza), and that's who he's addressing all this to the whole time.
First of all, the speaker of "Skunk Hour" is stuck on an island. We find this out right away. So his human interaction is limited to who's stuck there with him and, judging by the way he describes his neighbors in the first part of the poem, those people aren't his best friends. Though the speaker seems to know a lot about what these folks are like from the outside, he doesn't seem to know the more intimate details of their lives. This leads us to draw the conclusion that, besides seeing them on a regular basis, he doesn't actually know them very well. When night rolls around, this becomes even more evident as he drives around looking for signs of human life, and finds nothing but skunks.
The speaker prefers to be alone because he doesn't want to face ridicule for his mental illness.
He's not actually alone. This poem was just a brooding, lonely moment. He really has tons of friends on the island.
Yes, the speaker of "Skunk Hour" knows the people of Nautilus Island. Yes, he lives there year-round while others come for summer then leave for the rest of the year. But while his permanent address is on Nautilus Island, and he's got a back porch to stare out from, we get the sense that he doesn't feel quite at home in this town. Simply the way he describes the place puts it at such a distance that it's hard to imagine he feels much comfort, or much fondness, for it at all. What makes a home is hard to define, but we think it's safe to say that home is not where you lay your head every night, but – yup, you guessed it – where the heart is.
The speaker is just like the other vacationers. He doesn't live there year-round, but has come back for one day during the off-season.
The speaker used to feel at home there, but now that the mystery person has left, he's feeling too lonely to feel homey.
Thematically, this is not the most important aspect of "Skunk Hour," but it's one that's clearly there, especially from the beginning, so it's worth our attention. Social status also seems to be one of many reasons our speaker feels so distant from the other islanders – they're caught up in money and status while he couldn't seem to care less. Check out the beginning of the poem. Before the speaker goes all inward and dark on us, he's painting a picture of the fancy, bourgeois lifestyle (or the desire for it), old money (and wanting to keep the newbies out), and the vacationers that use the island as their summer playground then duck out when the weather turns chilly. With that much attention to the issue of class at the beginning of the poem, it's certainly an important part of Nautilus Island's fabric.
Lowell is just poking fun at the old-fashioned preoccupation with class. The social status is all in the heads of these characters, and doesn't really exist in real life.
Class issues and envy are the reasons for our speaker's feelings of loneliness and madness.