Phrase used to describe extremely hot and humid weather, such as the jungles of Vietnam, where it is 100F and 100% rH (relative humidity). These conditions present an intolerable combination, where the body is unable to cool off by evaporation of sweat because of 100% humidity. This can result in heat stroke and possibly death.
This summer's fixing to be one long Vietnam Combo...
by X2v34S July 15, 2010