The Khmer Rouge was communist in the much the same way as the Nationalsozialistische Deutsche Arbeiterpartei was socialist.
You can find quotes from prominent western leftists pontificating that the Khmer Rouge may finally get communism right. Their praise continued even as they watched the death marches out of Phnom Penh.
At the height of the cold-war, the US government supported the Khmer Rouge. On the other hand, the actually socialist (at the time) state of Vietnam invaded Cambodia and overthrew the Khmer Rouge. There might be a reason for that.
Is this another one of those "true communism has never been tried" posts that inevitably crop up?