Mister X and Mister Y

A couple of gentlemen, whose last names are X and Y, exchange polite banter, in which they frequently call each other "Mister X" and "Mister Y."

Often done by Those Two Guys or Those Two Bad Guys. (Our self-demonstrating description for Those Two Bad Guys does this.)

Comic Books

 * Mr. Shytte and Mr. Pysse, two royal guards attending Queen Gloriana, in The League of Extraordinary Gentlemen.

Fan Works

 * In Harry Potter and the Methods of Rationality, Crabbe and Goyle are faithfully following minions clichés and call each other "Mr. Crabbe" and "Mr. Goyle".

Films -- Live-Action

 * Those Two Bad Guys in Diamonds Are Forever always call each other Mr. Wint and Mr. Kidd.

Literature

 * Those Two Bad Guys in Neverwhere: Mr. Croup and Mr. Vandemar.
 * Those Two Bad Guys in The Truth: Mr. Pin and Mr. Tulip.
 * Those Two Bad Guys in Hamish X: Mr. Candy and Mr. Sweet.
 * Those Two Bad Guys in Peter Straub's story Mr. Clubb and Mr. Cuff.
 * Invoked by "Mr. Clock" and "Mr. Pink" in Redemption Ark when trying to intimidate someone, although it doesn't quite work out like they expect.

Live-Action TV

 * The League of Gentlemen, as a Shout-Out to Diamonds Are Forever, has a pair of surveyors who call each other Mr. Wint and Mr. Kidd.

Music

 * The song "Mister Gallagher and Mister Shean" by Ed Gallagher and Al Shean. Probably the Trope Maker; certainly the exchange "Absolutely, Mr. Gallagher?" -- "Positively, Mr. Shean" became a popular meme.

Theater

 * In The Golden Apple, shifty stockbrokers Mister Scylla (played by the same actor as Menelaus) and Mister Charybdis (alias Hector) do a pastiche of the Gallagher and Shean number.
 * In 1776, when John Adams and Thomas Jefferson are arguing over who will write the Declaration of Independence they refer to each other as Mr. A and Mr. J.
 * Classic Vaudeville Schtick: e.g. Mr. Bones and Mr. Jones, done by such as... Mr. Gallagher and Mr. Shean.

Web Original

 * Bok the Neutral has Doctors Diolen and Steerpike.
 * The Those Two Bad Guys page.

Western Animation

 * Mr. Wink and Mr. Fibb (parodies of Wint and Kidd) from Codename: Kids Next Door.
 * Mr. Doe and Mr. Cardholder, the mysterious OSI agents, in The Venture Brothers.
 * Mr. Touch and Mr. Go on Teenage Mutant Ninja Turtles 2003.