I'm omitting common logic snafus and bad CG. This is basic stuff that continue to elude most films:
  1. Wigs
  2. Old age make-up
    See also: young age make-up. Exception: Max Von Sydow in THE EXORCIST. For years afterward I'd see Von Sydow in movies and think, "he's still alive?"
  3. Composite "old" photos of the cast
    Exception: the prom pic of Rosamund Pike and Neil Patrick Harris in GONE GIRL.
  4. Actors' body language during greenscreen driving scenes
    They're not looking at the road, their hands are just resting on the steering wheel, which they never turn. No stops at intersections.
  5. Severed heads
    Thanks to Snopes.com, I had the misfortune to see an actual severed human head. It looked fake too. Game set match, heads.