It was at a party, and my friend X.Y. tried to crush a beer can against his forehead and failed. I don't mention his name because of the humiliation.
Not humiliation because of the failure, but because of what happened next.
I said to him, "You are such an idiot."
He replied, "Compared to you I am."
"That's right," I said. "Compared to me, you are."
It was hard for him to come back after that one.