I have watched a fair amount of disturbing films but most of them I don't really recommend watching
The only one I would really recommend are
Man Bites Dog (not too disturbing honestly other than that scene)
Angst (Similar to Man Bites Dog)
Occult
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There are some films I've watched that are more disturbing
Sweet Movie, The Piano Teacher, Antichrist, Kung-Fu Master, Salo. But I really wouldn't recommend anyone watch them especially the last two.