No gore needed, the most unsettling and gruelling scene imo is cold, clinical and understated; transferring true fear and helplessness on to the viewer in the most mundane way:
Spoilers if you haven't seen 'Michael Clayton (2007)' yet:
Devoid of humanity, no apparent eye contact, no attempt to comfort him or ease him into it. Not even a chance to get lost in the emotion of bargaining and chaos, but a sudden ninety seconds of calm to process the end.
Just,
'this is it'.. they might as well be furniture removal men.
If we're talking visceral, brutal violence in a more literal sense then probs the latter scenes with Jennifer Lawrence and the baby in
mother! (2017).
That said, I'm never really "shocked". It's more the implication of what's happening on screen rather than the violence or gore itself.