Bold Seagull
strong and stable with me, or...
Alien visitations - if the universe is as big as claimed, then it is a near certainty that they wouldn't be able to visit.Moon landings - not particularly likely the 1969 one happened, no. Too many Hollywood people involved in early NASA.
Alien visitations - if the universe is as big as claimed, it is near impossible that we haven't had visitors
Aliens stored in Area 51 - not seen any compelling evidence that this is the case so this one might well be false
9/11 - may or may not have happened as described, but the executive arm (the CIA) of the yankee banks as well as the US govt had the strongest motifs to make it happen
"Mainstream" theories that seem unlikely: flat earth, the Jewish global conspiracy (there is a global conspiracy but it doesn't have any ethnic or religious origin), Marxist conspiracy theory (the idea that 'socialists' and 'communists' are taking over the world is... a funny one as it would serve no purpose), WW2/holocaust denial (politically a far more complex war than people think, but it did indeed happen and so did the killings of millions of jews).
It's not just size either, it's time. The Earth is 4.5 billion years old. It pretty much took 4.5 billion years for intelligent life to evolve on Earth. The universe is 13.7 billion years old. So the universe is actually only 3 x older than it took intelligent life to evolve on Earth.
So not only are you talking vast distance to travel in terms of visit, you are also talking about a vast coincidence of time.
While not strictly a science fiction film, one thing George Lucas got right was 'a long long time ago...in a galaxy far far away'.