The speaker of "Liability" tells everyone to stay away, and the reason is painfully simple: they already dislike themselves. Each pair of lines heads off a reaction before it can happen. Hate me, and it won't hurt, because I hate me too. Pity me, and I've done that already. Even love is turned down, since the speaker expects it to fade once the other person gets tired, and that loss would hurt more than never being loved at all.
The tone is flat and matter-of-fact, which makes it sadder. There's no anger or pleading, just short, calm sentences, as if the speaker has gone over this many times. The final lines try to wave away concern ("don't worry about me"), yet calling themselves "a liability" shows how deeply they see themselves as a burden. The mood is bleak and guarded, though the refusal of help also reads like a quiet way of protecting themselves from being let down.