Once upon the time it really happened.
Me: What do you think, Mr. Everett’s follower, when are your teachings going to be taught in most schools?
Him: Later in this century, I am sure.
Me: In which Everett branch will this be, sear?
Him: In the averaged majority of them all!
Me: Really? In the averaged majority? Won’t this average mainly be shaped by the most radioactive post nuclear war branches, since they so quickly reproduce?
Him, already branched away.
You can use this handy logical entrapment for those people just about every time you meet one of them. Have fun!
Actually, your job will usually already be done after the second question. Not everyone of them will try to escape through the “averaged whatever”, but branch away from the debate right there. They preach the splitting of the whole Universe every time something quantum occurs. Which is about many times every nano second. They say the Universe divides like a bacteria, only much, much faster. They call the “petri dish” Multiverse and every bacteria an “Everett branch”, dividing further. No branch is special, all are of an equal status. In some of the branches the Roman Empire is still alive and well. In most, there are no humans. And so on and on.
Still, they hope to teach this in every school inside THIS world, later in the 21st century. They already do it in some.