Them yellow men wearin' black pajamas, they wanna harm us
The Khmer Rouge (Pol Pot’s Cambodian Communists) uniform. They wore black uniforms that were like pajamas. Thus, yellow men (Asian people, in this case Cambodians, as Cambodia was specified earlier in the verse) wearing black pajamas.
Vietcong soldiers, as opposed to Khmer Rouge, dressed as civilians to put American soldiers at dismay, which (along with the fact that omen and children would attack you) led to the killing of all people.
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