Across whole show

Frasier: Roger, at Cornell University they have an incredible piece of scientific equipment known as the Tunneling Electron Microscope. Now, this microscope is so powerful that by firing electrons you can actually see images of the atom, the infinitesimally minute building blocks of our universe. Roger, if I were using that microscope right now, I still wouldn't be able to locate my interest in your problem.

Kisses Sweeter Than Wine (series 3)

[Martin sees Frasier has a lot of cuts on his face from shaving.]

Martin: I thought you were just going to slit your wrists. Looks like you went for death by a thousand cuts.

Frasier: I cut myself shaving because I was shaving without water. Why was there no water? Because I had to move your chair, which gouged the floor, which made me call for Joe, who found bad pipes, which called for Cecil, who ate the cat that killed the rat that LIVED IN THE HOUSE THAT FRASIER BUILT!!

Sleeping with the Enemy (series 3)

Daphne: Oh, come on now, Dr Crane. It's not like men have never used sex to get what they want.

Frasier: How can we possibly use sex to get what we want?! Sex IS what we want!

The Candidate (series 2)

Daphne: It makes me glad we don't have so many guns in England.

Frasier: You don't need guns, you have kidney pie.

Seat of Power (series 2)

Frasier: You know the expression "Living well is the best revenge"?

Niles: Wonderful expression. I just don't know how true it is, you don't see it turning up in a lot of opera plots. "Ludwig, maddened by the poisoning of his entire family, wreaked vengeance on Gunther in the third act by living well."

Caught in the Act (series 11)

[Frasier tries to convince Niles that sleeping with Nanny G is the right thing to do.]

Niles: Did you say something? Your penis was talking so loud I couldn't hear!