A
compliment deliberately worded such that the indirect meaning is actually an
insult. Most left-handed compliments follow the pattern of expressing
admiration or
approval on the "compliment" side, then bringing up the "insult" side as a comparison or
afterthought:
"You look splendid today, Marcie! Nobody would ever guess you're 45."
"Hey, that's a great looking shirt, Tim! You can barely see your beer-belly."
Sarcasm is a large component in the left-handed compliment.
The more the aggressor knows about the target, and their particular weaknesses and sensitivities, the easier it is to deliver a left-handed compliment.