It's really all in the phrasing, isn't it? A backhanded compliment, or an issuance of approval that simultaneously tears someone else down, is no compliment at all. Having said that, I compliment parents all the time when their children are kind, well-behaved citizens of my classroom (or great students, responsible, etc). A true compliment should, IMO, focus on what the receiver is doing right, not what others are doing wrong.