What are Malaprops?

Mrs Malaprop, a character in in Richard Sheridan’s play The Rivals, gave us such gems as, “Oh, there’s nothing to be hoped for from her! She’s as headstrong as an allegory on the banks of the Nile.” and “If I reprehend anything in this world, it is the use of my oracular tongue, and a nice derangement of epitaphs!”
Substitute aligator for allegory, apprehend for reprehend, vernacular for oracular, arrangement for derangement, and epithets for epitaphs.
The French phrase mal à propos means inappropriate or ill-suited. The play popularized the term malapropism, and the device is still popular with humorists.
“No his uncle was not a businessman. He was a civil serpent.”
“He was served an erotic dish.”

""Our watch, sir, have indeed comprehended two auspicious persons." - Constable Dogberry in Much Ado About Nothing
“The law I sign today directs new funds and new focus to the task of collecting vital intelligence on terrorist threats and on weapons of mass production”
The last was uttered by George W Bush, a master malaprop or avid acyrologian.
Here’s another of his:
“Anyone engaging in illegal financial transactions will be caught and persecuted.”

Malapropism is also called Dogberryism or Acyrologia, but be careful and don't use these words in a sentence to mean 'defficiency of Vitamin B (beriberi)' or to mean 'fear of heights (acrophobia)'!