Garnett allegedly crossed the line during a Celtics win over the Pistons in 2010. After the game, Detroit forward Charlie Villanueva took to Twitter, alleging that Garnett called him a “cancer patient.” 

Villanueva suffers from alopecia universalis, a disease that causes hair loss. Garnett denied having called him a cancer patient, and issued the following statement:

"I am aware there was a major miscommunication regarding something I said on the court last night. My comment to Charlie Villanueva was in fact: You are cancerous to your team and our league. I would never be insensitive to the brave struggle that cancer patients endure. I have lost loved ones to this deadly disease and have a family member currently undergoing treatment. I would never say anything that distasteful. The game of life is far bigger than the game of basketball."

Even if Garnett was telling the truth, why would you even use that terminology with someone like that? This was one of the lower moments of Garnett’s career. But the next one was perhaps even lower.