In Chögyam Trungpa's teachings, "idiot compassion" refers to a misguided form of kindness that stems from the three poisons of Buddhism: grasping, aggression, and delusion.
It's a compassion that avoids difficult truths, reinforces unhealthy patterns, and ultimately doesn't help the person in need. Instead of genuine empathy, it's driven by a desire to feel good, avoid conflict, or manipulate others to feel better about oneself.