Band of Brothers, when the Americans liberated the few remaining survivors of the hellish nazi death camp and were ordered to keep the prisoners there as they were all so close to death that eating normal sized rations could kill them. If I recall correctly, it was an American of German descent that translated this to the prisoners. Essentially, the liberators seemed for that moment in time to became the enslavers. I don't think I have what it takes to do that. It was one of the most horrible sights I had ever seen.
Another one that gets me is the entire movie "Requiem For a Dream." I feel so horrible for Sara Goldfarb every time I watch that. In the beginning, when Harry is stealing the TV and all the way through towards the end, when she's locked up in the mental ward getting shock treatments.