a coined variation of
knock someone
dead, meaning to impress, dazzle or delight someone greatly. To
knock someone
dead literally means to
cause somebody to die by delivering a forcible
blow (a
knock), as with an
object, one's
hand, etc. Kill is used here as an intensification of
knock and figuratively means to
overwhelm someone by making an irresistible or very strong impression on them, as by causing astonishment, amazement,
admiration, etc.
Dead as used here means with an almost
complete, sudden ceasing or stoppage of
motion, as in "he stopped
dead when he
saw the robber."