It's like the second most famous scene in When Harry Met Sally... (after "I'll have what she's having"):
Sally: "Well, if you must know, it was because he was very jealous and I had these days-of-the-week underpants."
Harry: "Errrr. Sorry I need a judge's ruling on this. Days-of-the-week underpants?"
Sally: "Yes. They had the days of the week on them and I thought they were sort of funny. And then one day Sheldon says to me, 'You never wear Sunday.' He was all suspicious— where was Sunday? Where had I left Sunday? And I told him and he didn't believe me."
Sally: "They don't make Sunday."
Harry: "Why not?"
Sally: "Because of God."
Photo courtesy of RD