I'll have to go old school and say the scene in the original Texas Chainsaw Mass. Where it's the first guy to get killed with the hammer or mallet in the doorway when Leatherface first makes his apperence, because it's the most realistic death scene in a movie. And also the nanny in the first Omen movie that hangs herself at Damien's birthday party, because it scares the shit out of my girfriend.