A spoonerism is an occurrence of speech in which corresponding consonants, vowels, or morphemes are switched between two words of a phrase. These are named after the Oxford don and ordained minister William Archibald Spooner, who reputedly did this.
An example of spoonerism on a protest placard in London, England: "Buck Frexit" instead of "Fuck Brexit".
Spooner as caricatured by Spy (Leslie Ward) in Vanity Fair, April 1898.
Caricature of Charles H. Workman. The accompanying biography reads, "The only part of him which gets tired is his tongue, and occasionally the oft-repeated lines have got muddled. 'Self-constricted ruddles', 'his striggles were terruffic', and 'deloberately rib me' are a few of the spoonerisms he has perpetrated."
William Archibald Spooner
William Archibald Spooner was a British clergyman and long-serving Oxford don. He was most notable for his absent-mindedness, and for supposedly mixing up the syllables in a spoken phrase, with unintentionally comic effect. Such phrases became known as spoonerisms, and are often used humorously. Many spoonerisms have been invented and attributed to Spooner.
Spooner in 1924
Spooner as caricatured by Spy (Leslie Ward) in Vanity Fair, April 1898