"kiss of death"

hi there
Does anybody can tell me meaning of "kiss of death"
Thanks

KISS OF DEATH - "unwelcome support from an unpopular source, occasionally engineered by the opposition.The phrase is derived from the kiss of Judas and the betrayal of Christ. It is also described as coming from a gangland custom called 'omerta,' said to have begun in Sicily. 'In the mobs,' wrote Russell Baker, 'a kiss from the boss is tantamount to arriving at the office one morning and finding your rug gone.'" From Safire's New Political Dictionary by William Safire (Random House, New York, 1993).