A new kid arrives in class, and the speaker can't help noticing how well he fits in. He's nice, funny, and good-looking, and people keep telling the speaker he's a "better version" of them. The poem is about what that comparison does to someone's sense of self.
The speaker lists the differences one by one: he's funnier, more athletic, nicer, happier, "actually attractive." That last phrase stings the most, because the word "actually" suggests the speaker doesn't think they have ever counted as attractive. The image of a "defected clone" makes it worse, as if the speaker is a faulty copy of someone who turned out better. By the end, the words get blunt and self-critical: "Ugly," "Mess-up," "mistake."
The mood is quiet and heavy. The short, flat lines read like someone talking themselves down, and the poem never offers comfort. It simply lets the hurt sit there, which makes it feel honest and painfully familiar.