But on forum groups, in YouTube comments, and in person at conferences, flat-Earthers are deadly serious. And one of the biggest sources for renewed interest in flat Earth is YouTube, according to research by a team at Texas Tech University.
"YouTube is where the first flat Earth videos were posted around 2014, which launched the movement that we see today," Alex Olshansky, a researcher from Texas Tech who specialises in science communication and misinformation, told ScienceAlert.
"Because YouTube's algorithms recommend videos that are similar to what you are already watching, many people who were watching other conspiracy videos, found a flat Earth video in their recommended feed and proceeded down the rabbit hole."
Back in 2017, the research team went to the first Flat Earth International Conference and conducted in-depth interviews with 31 participants. The questions were geared to understand how their belief started, their understanding and curiosity of science, and their self-perceptions.
The results are fascinating, and aren't quite as easy to mock.
"Many have lost friends, and even family members and jobs over their beliefs and convictions," explained Olshansky.
"A common misconception is that many of these people didn't have communities beforehand or were social outliers … I would say that the majority had their own communities, were then rejected by those communities because of flat Earth, and then subsequently embraced the flat Earth community."
It's not just fringe conspiracy theorists that can start believing the world is flat. The researchers have found that many different types of people can be swayed by the arguments of flat Earth.
"One of the master's students, after watching one of the YouTube videos, told me that he began to question what knowledge he had taken for granted," said Olshansky.
"Our recent study, for instance, found that whereas people who are very low in conspiracy mentality completely rejected the arguments that appealed to religion and conspiracy, the more scientific-sounding arguments made in these YouTube videos were seen as presenting reasonably strong arguments."
And this is where the medium of online video truly comes in – nearly all the people interviewed said that they first got information about flat Earth from YouTube.
"YouTube also represents for them an avenue for real truth, given their mistrust of mainstream media and institutions. They see YouTube as a voice for truth-seekers and truth-tellers that you can't find anywhere else," said Olshansky.
"Most of the flat-Earthers I spoke with said that they initially thought the idea was crazy, then tried to debunk many of the claims they heard, and when they were unable to, became more and more convinced that Earth was not a spinning ball."
According to Olshansky, there are ways to show people Earth is in fact spherical, and fight disinformation in the process.
"We are calling on scientists and/or science advocates to make their own YouTube videos that answer many of the questions raised by flat-Earthers," he told ScienceAlert.
"Not in a debunking way or a sarcastic or patronising way, but in a genuine attempt to show how we can actually answer these questions properly with convincing evidence or demonstrations."
While there can indeed be legitimate reasons to distrust people in power and be skeptical about claims you hear on mainstream media, we do have many lines of evidence showing Earth is not flat, including some cheap ways of proving it yourself.
We have plenty of photos of our spherical planet - and their source, various space agencies from around the world, work for different (often rival) governments and even private organisations, so they would need an extraordinarily compelling reason to form a conspiracy together.
YouTube explained in a recent blog post that it will step up its game when it comes to its controversial recommends feature, and will begin reducing recommendations for videos such as flat Earth theories, or miracle cures for illnesses.
Although this seems like a great move, it may be too little, too late from the multi-billion dollar company.
The most recent research has been presented by Asheley Landrum at the American Association for the Advancement of Science in Washington DC.