Malapropism

A malapropism (from French mal à propos, "ill to purpose") is an incorrect usage of a word by substituting a similar-sounding word with different meaning, usually with comic effect. The term comes from the name of Mrs. Malaprop, a character in Richard Brinsley Sheridan's comedy, The Rivals (1775), whose name was in turn derived from the existing English word malapropos, meaning "inappropriately".

Examples

Attributed

"He's as headstrong as an allegory on the banks of the Nile." (i.e. alligator) — Sheridan, The Rivals
"He is the very pineapple of politeness." (i.e. pinnacle) — Sheridan, The Rivals
"If I reprehend any thing in this world, it is the use of my oracular tongue, and a nice derangement of epitaphs!" (i.e. apprehend; vernacular; arrangement; epithets) — Sheridan, The Rivals
"I've gotta consecrate myself on this newspaper." (i.e. concentrate). — All in the Family (*Note the non-standard use of the reflexive, indicating the Yiddish-German influence on New York City speech.)
"If it's any consolidation..." (i.e. consolation) — Ken James
"I want to be effluent mum!" "You are effluent Kimi..." (i.e. affluent) — Kath and Kim
"What are you incinerating?..." (i.e. insinuating) — Galton and Simpson, Steptoe and Son ("Doodlebug over Shepherd's Bush")
"You could have knocked me over with a fender." (i.e. feather) — Jane Ace, one of many malaprops she used on the old-time radio comedy series, Easy Aces.
"I heard the sea is infatuated with sharks" (i.e. infested) - Stan Laurel in The Live Ghost.
"V.D. Day!" (i.e. V-E Day) — Edith Bunker (as played by Jean Stapleton), on television's All in the Family.
"My nipple."(i.e. dimple) — Malaysian singer Siti Nurhaliza when asked what is her best facial feature.
"My magnificent octopus!" (i.e. magnum opus) — Baldric, Blackadder the Third
"Worst case Ontario..." (i.e. scenario) — Ricky, Trailer Park Boys
"She's just going through a phrase." (i.e. phase) — Ricky, Trailer Park Boys
"I might just fade into Bolivian, you know what I mean?" (i.e. oblivion) — Mike Tyson
"I really dig Hannibal. Hannibal had real guts. He rode elephants into Cartilage." (i.e. Carthage) — Mike Tyson
"Pardon me for protruding" (i.e. "intruding") — Dorrie Evans, Number 96, also used prior to this in the 1968 film of Chitty Chitty Bang Bang by one of the Vulgarian spies.
"I'm braless" (i.e. barless) — Ziva David, NCIS
"I'll hunt you and shoot you down like a duck." (dog) — Buford "Mad Dog" Tannen, Back to the Future III
"I can't even phantom how that must feel!" (i.e. fathom) — A young girl on a T-Mobile commercial during which her father was strapped into a chair while she used up her "anytime minutes."
"I already made like affinity of those at scout camp." (i.e. an infinity) — Napoleon Dynamite
"It's a moo point." (i.e. moot) — Joey Tribbiani, Friends
"It's a moo point" (e.g. An argument that is neither true or false - Zen and the Art of Motorcycle Maintenance, Robert Pirsig, 1974)
"Tell her I'm good-looking and I'm rich and I have a rapist wit." (i.e. rapier) — Lloyd Christmas, Dumb and Dumber
"I am not going to make a skeptical out of my boxing career." (i.e. spectacle) — Tonya Harding

Unattributed

"He missed that field goal by a microcosm." (i.e., micrometre)
"Then he laid prostate on the ground." (i.e., prostrate)
"You know I get ravishing when I play indoor cricket." (i.e. ravenous)
"I feel like a social piranha." (i.e., pariah)
"Don't talk about the baby; she had a misconception." (i.e., miscarriage)
"It's been a pressure." (i.e. pleasure)
"...tapered to suit your needs." (i.e. tailored)
"I want everyone to conjugate over here." (i.e. congregate)
"It'll only take a mint" (i.e. minute)

Dogberryisms

It may be more appropriate to call such confusions "Dogberryisms" after Sergeant Dogberry in William Shakespeare's Much Ado About Nothing, who was making them almost two centuries earlier. Some examples include:

"Comparisons are odorous." (i.e., odious)
"Our watch, sir, have indeed comprehended two auspicious persons." (i.e., apprehended; suspicious)
"Thou wilt be condemned into everlasting redemption for this." (i.e., damnation)

Other characters from literature who used malapropisms

In Neil Simon's play Proposals, Vinnie Bavasi is a South Florida Mafia type who speaks in malapropisms.
The character of Launcelot in Shakespeare's The Merchant of Venice uses numerous malapropisms in one scene to create comic relief.
The characters of Biff Tannen (Back to the Future and Back to the Future Part II), and his great grandfather Buford 'Mad Dog' Tannen (Back to the Future Part III) often use malapropisms for comic effect, although they are unaware they are doing so.
The character of Ricky (Trailer Park Boys) uses malapropisms on a regular basis, he calls sasquatches Sasketchewans, talks about Catch 23 situations, and says his daughter is just going through phrases.
Mayor Shinn in The Music Man is prone to embarassingly misusing terms, including "not one poop out of you, Madam."
Elbow from Shakespeare's Measure for Measure uses many malapropisms for comic effect, which other characters such as Pompey mock.