Left-Handed Compliment Meaning

(idiomatic) A complimentary remark which is ambiguous or ineptly worded, so that it may be interpreted as having an unflattering or dismissive sense.

Example: 1921, E. Phillips Oppenheim, Nobody's Man, ch. 16:
  "We have sat through the whole of dinner and not once mentioned politics."
  "You made us forget them," Tallente murmured.
  "A left-handed compliment," Jane laughed.
1964 Oct. 30, "The Morning After," Time (retrieved 7 Oct 2013):
  In a somewhat left-handed compliment, UN Secretary-General U Thant described Russia's new bosses as "competent and unpretentious."
2006 March 19, David Orr, "On Poetry: Samuel Menashe—New and Selected Poems," New York Times (retrieved 7 Oct 2013):
  [C]alling someone a "neglected master" makes for one hell of a left-handed compliment.