You've probably heard of the very precise, scientific unit of measure called the "buttload." Usages might include, "I'd love to hang out, but I have a buttload of homework tonight." Or, "I cleaned out my closets and dropped off a buttload of clothes at the thrift store."
But where did this particular butt-based unit of measure come from?
No, You Started It
Some assert that "buttload" was first used in print in the novel "Los Angeles Without a Map" by Richard Rayner in 1988, and that it's chiefly used in the United States. Fair enough. But what about its close yet more vulgar cousin, sh*tload? Merriam-Webster has that one going as far back as 1954, but they still blame Americans for it. The Brits had cleaned this one up by the 1990s, exchanging it for "shedload."
As long as we're looking up words, what about "boatload?" Could that have led to the "buttload" phenomenon? Maybe, but boatload has been in use since at least 1625, when it was used by explorer John Davis as recounted by Samual Purchas in "Purchas His Pilgrims." It really does just mean the number of people a boat can hold, and there don't seem to be any clear lines between boatload and buttload across more than 400 years.
But There Is a Butt
While "buttload" may be a rough estimation of a large amount, there is a unit of measure for mass called a butt. It's an old unit first used in medieval times, but it's hardly more precise than "buttload."
A butt is a cask that holds liquids, like a barrel. It could contain anywhere from 108 to 140 gallons (409 to 530 liters), which is indeed a lot. But it's probably not the origin of "buttload," as there don't seem to be any connections between a medieval barrel in Britain and the use of the term in late 20th-century America.