My personal one that only matters to me is that all of the big law firm scenes in Michael Clayton were filmed in my old firm’s offices, and I find it funny every single time that Clayton, described as an associate, has a corner office that actual firm partners would knife each other for.
We all know the "Viggo broke his toe" story but what's another movie fact you're personally compelled to bring up every time without prompting? For me, it's the fact that Robin Tunney is wearing a wig in The Craft because of having just shaved her head to save her job filming Empire Records.