Don't leave a piece of jewelry at his house so you can go back and get it later; he may be with his real girlfriend.

Framed as a blunt, comic “rule,” the line satirizes a familiar dating tactic: leaving a personal item behind to manufacture a reason for future contact. Sedaris flips the maneuver into a cautionary joke about self-deception and romantic competition—if someone is not truly available or committed, the ploy can backfire by revealing you are not the primary partner. The humor comes from its practical specificity (jewelry, his house) and the sudden sting of “real girlfriend,” which punctures fantasies of control. Beneath the punchline is advice about boundaries and clarity: don’t rely on contrivances to secure attention from someone who may already be attached.