The mirror stabbing scene from Donnie Darko.
I have dissected that movie left and right, up and down, and still can not figure out any signifance to it aside from personal speculation from other people. Closest thing I can figure out is that Frank was torturing him, so he thought stabbing the reflection in the eye would kill him. That, or he was just sort of...highlighting...the area that Frank had an injury to.
That, and Frank, although awesome (as evidenced by the Frank posters/figures/etc all over my room), gives me the creeps worse than ANYTHING I have seen. Ever. Still love him though.