If this phrase sounds a bit campy, perhaps that's because it's been used as a title for film noir, heavy metal albums and vampire novels. But the original use was as serious as it gets.
That kiss of death was given by Judas to Jesus. It identified Jesus for the arresting soldiers who would send him to his crucifixion.
Today, kiss of death names something an act or an association that ultimately causes ruin.
For example: "The Treasury Department quickly shelved plans to publish the list [of banks receiving aid] so as to avoid giving the kiss of death to banks who are not on it." (New York Times, Oct. 2008)