Damn somebody/something with faint praise
Definition 1 of 1
Pro Tip 1/3Subtle Criticism
Understand that 'damn with faint praise' subtly suggests disappointment or disapproval rather than outright condemning. 
Her performance was called 'competent,' damning it with faint praise.
Pro Tip 2/3Sarcasm Sense
Be aware that this phrase can be sarcastic, implying the opposite of the praise given. 
He's 'remarkably average,' she said, damning with faint praise.
Pro Tip 3/3Cultural Nuance
In some cultures, direct criticism is rude, so this phrase is a polite way to express a negative opinion. 
Your idea is 'interesting,' he said, damning it with faint praise.