Although the word “malarkey” has been in use since 1929, its origin is still a mystery. The Merriam-Webster Dictionary defines "malarkey" as foolish ideas or words. It can also mean foolish or insincere talk.
VP Biden's remark
Although a little antiquated, the word is still regularly used in the U.S. Interestingly, it became one of the most looked-up words after the vice-presidential debate between Joe Biden and Paul Ryan in October 2012. Vice President Biden used "malarkey" twice during the debate to show his disagreement with what U.S. Rep. Ryan was saying. In one instance, Biden used the word after Ryan answered a question regarding criticism of the way the Obama administration had responded to the Benghazi attack on September 11. That simple remark drove thousands of people to look the word up online, which resulted in “malarkey” becoming one of the 2012 Words of the Year on Merriam-Webster's website.
Some ideas on its origin
Ben Zimmer, a U.S. language commentator, lexicographer, and linguist, has alleged that the word was first used by Irish Americans. Zimmer then went on to cite Michael Quinion, a British writer, etymologist, and the author of World Wide Words, in his claim that the word's origin is still unknown. (Zimmer added that the word was popularized by Thomas Aloysius Dorgan, a cartoonist. Aside from “malarkey,” he also popularized "kibitzer" and "hard-boiled" through his cartoons.)
Not everyone agrees with Zimmer’s conclusion. According to The Economist, if the word was popular among Irish Americans, it should have Gaelic roots rather than American. However, “malarkey” was already in common usage in America long before it ever made its way around the U.K.
When it first appeared in the U.S., “malarkey” had different spellings: mullarkey, malachy, and malaky. Eric Partridge, who published A Dictionary of Slang and Unconventional English in 1937, theorized the word could have come from "malakia," a modern Greek word. However, his theory was not considered a credible one. Some other theories were equally far-fetched. One theorist pointed out that it could have originated from the Irish family name Malarkey, which was renowned for its glibness of speech, but this suggestion contained no information about the origin of the word. Another British lexicographer of slang, Jonathon Green, asserted the word could have come from the Irish term, mullachan, which is a description for a ruffian or a boy who is strongly built. But that, too, was deemed unlikely.
Therefore, the past remains murky, and for now, we have to simply accept that the origin of the word “malarkey” remains unknown and that all the suggestions about its possible origin are just… malarkey.