Black people are like sperm They're good at running, most of them are unsuccessful, and they get killed by white cells.
I don't understand it. Can you explain why you brought this up?
White people are like white blood cells. They do most of the work in your body, and when black people get along with them, they call them racist.
Even positive stereotypes (ex: blacks are athletic) can still cause harm. Also, I think that joke implies that all white folks kill black folks, which is also a harmful stereotype.