Accidental Proposal: In Ride 'Em Cowboy, Willoughby (Lou) accidentally shoots an arrow into an Indian maiden's teepee. Tribal custom says this is a proposal of marriage and Lou and Bud spend much of the rest of the film running away from the bride-to-be and her tribe.
Adorkable: Often used in their movies: Costello's goofy, bumbling, buffoonish charm generally makes the women he meets fall for how adorable he is - despite being a goof Costello always gets the girl in situations where the two are involved in romance.
All Amazons Want Hercules: In Abbott and Costello Go To Mars, Lou falls in love with the Amazonian Queen of Venus, a love she reciprocates... until his inability to keep his hands off of her subjects, and his cohorts' foolish attempt at staging a palace revolt, gets them all shipped back to Earth.
It didn't help that the Queen showed her subjects holograms of the previous King, an attractive hunk; the ladies immediately lost interest in the dumpy Lou.
Bad Boss: Abbott's first character in Little Giant.
Berserk Button / Never Say That Again: The "Slowly I turned..." routine was used by Abbott and Costello several times: in the films Lost In a Harem with the trigger word "Pokomoko", and In Society with the trigger phrase "Susquehanna Hat Company", as well as in The Abbott and Costello Show on television, using the more traditional "Niagara Falls".
Butt Monkey: Costello most of the time. Abbott takes this role in The Time Of Their Lives.
The fate of Sgt. Collins in Buck Privates Come Home.
Cannot Spit It Out: Whenever Costello sees something that makes him flustered, he becomes hilariously tongue-tied and unable to explain it to Abbott.
Cassandra Truth: Played with in most of the horror spoofs - the monster or ghost (and in one case, Indian chief) terrorizes Lou, but only when Bud isn't around to see it. Naturally, Bud never believes Lou.
Chain of Corrections: Several of their routines fit this trope, none more famous than "Who's on First?." Played to perfection, the routine saw Abbott list the names of players on a baseball team to Costello, Costello constantly misinterpret the answers as non-responsive, Abbott correct him repeatedly and Costello becoming even more befuddled and confused to the point where, in the end he throws up his hands and says "I don't give a damn!" – unwittingly identifying the shortstop.
Crazy Jealous Guy: Dr. Jekyll in Meet Dr. Jekyll and Mr. Hyde. Made all the more disturbing by the fact that the object of his affections is his niece.
The Danza: In One Night in the Tropics (as well as many of their later works), they skipped the intermediaries and just played characters named "Bud Abbott" and "Lou Costello".
In Abbott and Costello Meet the Mummy, their characters were called "Peter Patterson" and "Freddie Franklin", respectively—at least according to the credits, which was the only place those names were used.
Dirty Coward: Costello was often this in films, especially when dealing with the Universal monsters. Abbott usually upbraided him for this, telling him to "Be brave like me!". Of course moments later the monster would return and Abbott would practically trample Costello on his way out the door.
Dirty Old Man: Dr. Jekyll, who wants to force his young niece to marry him.
Disney Death: Several of their films include a routine in which Abbott believes Costello has been killed and has a Heel Realization, lamenting how he treated his friend, while Costello listens and cries along with him. Once Abbott sees that he's all right, he instantly goes back to his old self and slaps Costello for getting him so worried.
Fun with Foreign Languages: In Lost In Alaska, Costello sees some Eskimos communicating in sign language and makes a few random hand gestures of his own. The Eskimo chief starts laughing, telling Costello, "You just told a funny joke!" Later, when Costello meets an attractive Eskimo lady, he tries to impress her by creating the same hand gestures he used before. She slaps him in the face; apparently it was that kind of joke.
Handy Cuffs: One sketch involves one of them getting handcuffed with his hands in front when he points out that he can still swing his hands around. He then asks his captor to show where the cuffs need to go; the captor puts his hands behind his back, gets cuffed, and the good guy escapes.
Hero Antagonist: The drill sergeant in Buck Privates and Buck Privates Come Home.
Mistaken for Terrorist: Bud and Lou in Buck Privates Come Home when demonstrating how the model of their friend's midget racer works to a bank manager. Lou revs it up backwards and it starts backfiring, making it look like he's firing a machine gun from outside the office.
Also, Abbott and Costello Meet The Killer, Boris Karloff, in which the killer is not Boris Karloff.
Perhaps also, Here Come The Co-Eds, in which the school in question is an all-girls school and so technically the girls there are not "co-eds."
Not-So-Harmless Villain: Costello's not the sharpest tool in the shed, but he's not quite as stupid as he looks either. Depending on the Writer, he sometimes has scenes where he skillfully outwits people who think he's just a moron - Whodunit in particular has him do this several times during the climax.
Obfuscating Stupidity: Very rarely, Costello is portrayed or merely implied as having this. Or more like he acts like a moron but he can be pretty quick when he wants to be.
An Odd Place to Sleep: In Buck Privates Come Home, Herbie (Lou) finds it too hot to sleep inside the apartment, he rigs up a makeshift hammock on the clothes line that runs between the buildings.
Precision F-Strike: The punchline to the "Who's on First" sketch is that the shortstop is named "I don't give a darn," a big enough deal at the time that they had to change it to "I don't care" when the routine was used in the film The Naughty Nineties.
Reaching Between the Lines: Lou keeps trying to make an important call but is obstructed by the operator who keeps telling him, "The line is busy". Eventually Lou gets so frustrated that he squirts a soda siphon down the mouthpiece and the operator gets squirted in the face.
Red Herring: In Abbott and Costello Meet The Killer, Boris Karloff, the Big Bad is actually the manager of the hotel where the film takes place, not Boris Karloff's character.
Self Offense: in Abbott and Costello Join the Foreign Legion and Abbott and Costello Meet Dr. Jekyll and Mr. Hyde.
Sequel: Buck Privates Come Home is, indeed, one of these to Buck Privates.
Shotgun Wedding: In Ride 'Em Cowboy, the Indians suggest forcing Costello into a "bow-and-arrow wedding".
The Show Must Go On: On the radio show Lou and Bud worked on, one day around the time they were working on Abbott and Costello Meet Frankenstein Lou came in for show late, very quiet, and went through his routines flawlessly but without speaking to anyone outside of the job, which was very unusual for him. Then at the end he said to his very young son, "That one's for you." He then explained to his fellow performers and the listeners at home that his son had drowned earlier that day, but not before Lou promised him that "Tonight you'll hear Dad on the radio." Lou kept his promise.
Tempting Fate: From Hit The Ice: "If I ever fall in love with another girl, I hope they hang me". Cue Costello seeing a pretty girl and the mail hook of a train catching him by the neck.
Tongue Tied: Several films have Costello needed to impart some important information, usually that the movie's villain is nearby. However, while he mimes speaking the words, he's so scared that he literally cannot make any kind of audible sound.
Took a Level in Jerkass: Abbott's selfishness and cruelty to Costello is taken Up to Eleven in Africa Screams, where is is nearly driven insane by greed upon discovering diamonds in the African jungle. He ends up being a victim of Laser-Guided Karma at the end when a friendly gorilla gives Costello the diamonds and makes him filthy rich, and Abbott ends up working as his elevator operator.
Vitriolic Best Buds: Onscreen, this was played straight. Offscreen, though, the "Best Buds" part was questionable.
The reason they have so few scenes together in Little Giant and The Time of Their Lives is because they were so estranged at that point, that was the only way they would agree to appear in the same picture.
Though their relationship was strained in their later years, there were a few moments of They Really Do Love Each Other, if you knew where to look. Abbott volunteered at Costello's charity as an attempt to bury the hatchet and, when Costello died of a heart attack, Abbott backed out of a revival project with Candy Candido playing Costello's role, claiming that there was no one who could truly replace Lou.
Weak-Willed: In Abbott and Costello meet the Invisible Man, a psychologist tries to hypnotize Lou Costello. Lou proves to be completely immune, but the psychologist accidentally hypnotizes himself. Lou's efforts to explain how this happened lead to him putting half the local police force under as well. Then Lou wakes him up, and managed to accidentally hypnotizes him again mere seconds later.
Who's on First?: In many of their routines, of which the trope namer is only the most famous.
Jerry Seinfeld referenced them a number of times on his show, most notably when George tries to explain his idea about 'a show about nothing'. He would also produce and star in an NBC special Abbott and Costello Meet Jerry Seinfeld.
Looney Tunes parodied them in three cartoons as "Babbit and Catstello". They also borrowed some of Lou's catch phrases and made them their own, like "I'm only three-and-a-half years old" and Bugs Bunny's "Gee, ain't I a stinker?"
In the "Vintage Steele" episode of Remington Steele a body is found in a vat of wine at the Costello Monastery. When Laura suggests they interview the abbot, Movie buff Steele quips "Ah...the Abbot of Costello".
If you didn't see some similarities between Ren and Stimpy and Abbott and Costello, you weren't paying close enough attention.
The Gummi Bears episode "Friar Tum" features a character named Abbot Costello.
The Khaavren Romances novel Five Hundred Years After has a passing mention of a famous farce, Who Dropped Her First?, set in a bedchamber laid out (reading between the lines) like a baseball diamond.
The Futurama episode "A Pharaoh to Remember" has a reference to Abbott and Costello Meet the Mummy.
Mother 3 features a duo of comedians named Lou and Bud as minor characters.
An anonymous email that has been circulating around the internet for many years casts Abbott as a tech-support operator attempting to explain to Costello that to stop his Windows PC he must click on the "Start" button.
In Australia, the days when Tony Abbott and Peter Costello were prominent members of the Liberal Party were a gift to political commentators across the country.
One episode of VeggieTales featured Larry and Mr. Lunt's characters having a battle of wits, with the riddle they must solve being presented by the Abbot of Costello. The riddle itself is a parody of the Who's on First? routine.
In the Batman: The Animated Series episode "Joker's Millions", Joker named his loyal pet hyenas Bud and Lou (previously only known as Harley Quinn's "babies"). This makes sense, given Joker's appreciation of comedy. The hyenas are given the same names in Krypto the Superdog.
A recurring segment on Square One TV featured Cabot and Marshmallow. Set backstage at a Vaudeville theater, the segments show Cabot getting the better of Marshmallow through a variety of math related tricks. Always started with a suitably altered version of Costello's catch phrase.
In the Sherlock episode "The Hounds of Baskerville", the Major snarkily tells Sherlock (who he's mistaken for a Conspiracy Theorist) that they have two aliens in their basement named Abbott and Costello.