Frasier: All right. I want her and she wants me.
Niles: She's married.
Frasier: Well, I married her first. "Till death us do part," as I recall. Now you may not take those vows seriously, but I do.
Niles: Will you listen to yourself?
Frasier: Oh, this is more than just sex, Niles. This is passion, kismet. A gift the gods bestow on only a chosen few. Wouldn't the real sin be to refuse it?
Niles: Isn't that your old second-piece-of-pie argument?
Frasier: Well, maybe it is, but I haven't had pie in six months!