I broke up with my girlfriend. She moved in with another guy, and I draw the line at that.

This is a characteristically Shandling-style one-liner built on deadpan understatement and a deliberately skewed sense of “reasonable” boundaries. The humor comes from treating an obviously relationship-ending event—one’s girlfriend moving in with another man—as if it were merely a debatable line in the sand, as though lesser infractions might be negotiable. The joke also plays with self-deprecation: the speaker implies he tolerated a great deal and is only now, belatedly, asserting standards. In miniature, it reflects Shandling’s comedic persona: anxious, self-aware, and wryly analytical about intimacy, turning emotional pain into a logical-sounding punchline.