Peoples bore me, (9)
That's right, Shmoopers. That's "peoples," not "people." That "s" really changes the tone of this line. The speaker here isn't talking about being bored by individual people. He's writing off entire groups—peoples. He finds all cultures boring. Imagine trying to go out to dinner with this guy. Mexican? Nope. Chinese? Nope. Yugoslavian? Not interested. He's bored by all of it.
Literature bores me, especially great literature, (10)
First, he writes off every single group of people in the world. Next to get the ax is "great literature." What gives? We get the sense that this guy has some kind of chip on his shoulder. It seems like the better something is, the less he's interested in it. So maybe the problem isn't with these things that bore the speaker. Maybe his boredom comes from within.
Henry bores me, with his plights & gripesas bad as achilles,
who loves people and valiant art, which bores me. (11-13)
Ay, there's the rub: the speaker is bored with himself (Henry). He's tired of his life. He's tired of his own "plights and gripes." (And we have to agree with you on that one, buddy. No one likes a complainer.) Interestingly, even though he's so, so bored by art and culture, he compares himself to the mythological warrior, Achilles. I guess even people who are bored with culture can't describe their boredom without referencing other elements of culture. So I guess we kind of need that culture stuff after all? Like, to communicate with each other? Ow, our brains hurt.