The controversy stems from Cathie Black joking about overcrowding in the schools on Friday.
"Could we just have some birth control here for a while. It could really help us a lot," she said.
But today nobody's laughing.
"Obviously, it was a joke. Nobody says it wasn't, but you don't make jokes like that when you have a massive overcrowding problem," Julie Menin of Community Board One said.
So today when Rev. Al Sharpton introduced the mayor at his annual MLK event, Bloomberg got booed.
"Come on! We're upset the choice he has made. You're choosing a business person to run an education institute," Gregory McMillan of National Action Network said.
"That lady he appointed - for education? She should never be talking about us black people need to stop having babies or need birth control," Sandra Hynson said.
In fairness to the chancellor, she never said a thing about race and birth control.
The mayor, though, deemed it bad enough.
"Cathie Black made a joke. Some people took it the wrong way. She has apologized. I think she'll learn slowly with time as did I," Mayor Bloomberg said.
This latest controversy comes as a recent poll gave Bloomberg his lowest approval rating ever, 37 percent -- but that was because of the big blizzard. His unpopularity today seemed tied solely to his new and controversial schools chancellor.