I guess I just prefer to see the dark side of things. The glass is always half empty. And cracked. And I just cut my lip on it. And chipped a tooth.

The line is a comic escalation of the familiar optimism/pessimism cliché about a “half-full” versus “half-empty” glass. By adding that the glass is not only half empty but also cracked—and that it causes immediate injury—the speaker turns ordinary pessimism into a self-aware, exaggerated worldview in which even neutral situations are interpreted as actively harmful. The humor comes from piling on misfortune in quick succession, suggesting a personality that expects disappointment and narrates it with biting wit. It also hints at how cynicism can become a protective style: if you anticipate the worst, you can claim control over being surprised by it.