In just three lines, this speaker makes a sharp and uncomfortable confession. A narcissist is usually someone in love with themselves, but here the speaker claims to be a different kind: one whose obsession with themselves shows up as hatred. The word "only" suggests they feel strange, even alone in this, as if no one else could be caught in such a twisted version of self-focus.
The poem's neat trick is that it points at a contradiction and lets it sit there. Hating yourself constantly still means thinking about yourself constantly. The speaker seems to know this, which adds a layer of self-awareness, maybe even self-mockery. They criticize themselves for criticizing themselves, and the loop never ends.
The mood is bleak but dryly witty. There is no big emotional outburst, just a flat, honest tone, and that calm makes the pain feel more real. It reads like a joke that isn't really funny.