The Kissinger Transcripts: A Verbatim Record of U.S. Diplomacy, 1969-1977, apparently includes:
Foreign Minister: The Cambodians want salt and fish. They want to barter for these items.
The Secretary: Did [Khmer Rouge commander] Ieng Sary impress you?
FM: He is a nice, quiet man.
Sec: How many people did he kill? Tens of thousands?
Mr. [Assistant Secretary Philip] Habib: Nice and quietly!!
FM: Not more than 10,000. That's why they need food. If they had killed every-one, they would not need salt and fish. All the bridges in Cambodia were destroyed. There was no transportation, no gas. That's why they had to chase people away from the capital.
Sec: But why with only two hours' notice?
Sec: What do the Cambodians think of the United States? You should tell them that we bear no hostility towards them. We would like them to be independent as a counterweight to Vietnam.
FM: Are you a member of the domino club?
Sec: I am.
FM: The outer, most exposed belt of dominos is Cambodia and Laos. Thailand is in the inner belt and is less exposed.
Sec: We would prefer to have Laos and Cambodia aligned with China rather than with North Vietnam. We would try to encourage this if this is what you want.
FM: Yes, we would like you to do that.
Sec: And then after we do it you can kick us around. You can call Ambassador Anan home and thereby keep the students happy.
FM: The right wing is what we really have to worry about, not the left.
[... much talk about Phan Hien's hairdo and some very nice real estate in Bangkok...]
Sec: You should also tell the Cambodians that we will be friends with them. They are murderous thugs, but we won't let that stand in our way. We are prepared to improve relations with them. Tell them the latter part, but don't tell them what I said before.
"murderous thugs": even six months into the reign of the Khmer Rouge that sounds a little rich coming from Kissinger.