Probably 'The Thing' and 'Robocop'. But then I saw scenes from 'The Thing' (the 80s version with Kurt Russell) again on Youtube... and it just made me laugh how fake some of those gory scenes looked.
And then there's 'Class Of 1999', about a bunch of ruthless cyborg teachers on a school in a dystopian future ruled by juvenile gangs. Kids getting chopped in half, people getting punched through the stomach with bionic fists, and a cyborg ripping into a young gangster's skull saying "I do enjoy molding young kids' minds". That movie disturbed me so much, when I saw it was announced to air in the TV-magazine, in a series of sci-fi movies my mother and I had been enjoying, I told my mother "I really do not want to see this movie".
And if it counts, 'End of Evangelion'. Just saw it, still gets me everytime. But it's really a part of the TV-series, instead of a stand alone film, but still.
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clarity of thought before rashness of action