A backhanded compliment
Definition 1 of 1
Pro Tip 1/3Detecting Sarcasm
Listen for tone and watch for facial expressions to catch the sarcasm behind a backhanded compliment. 
Her grin as she called his cluttered desk 'organized chaos' hinted at a backhanded compliment.
Pro Tip 2/3Hidden Insults
Understand that a backhanded compliment may hide an insult within what sounds like flattery. 
Saying 'You're not as slow as I thought' is a backhanded compliment implying low expectations.
Pro Tip 3/3Cultural Sensitivity
Remember, different cultures may interpret backhanded compliments differently; be mindful of context. 
In some cultures, 'You've lost weight!' could be a backhanded compliment offending the receiver.