Don't know if it's the best, but one of the most disturbing (and downright scary) films I've ever seen is Henry: Portrait of a Serial Killer, a film based loosely on the crimes of Henry Lee Lucas.
"Growing up my dad was like 'You have a great last name, Galifianakis. Galifianakis...begins with a gal...and ends with a kiss...' I'm like that's great dad, can we get it changed to 'Galifianafuck' please?" -- Zach Galifianakis
