How do you kill 500 flies in one hit? Slapping an Ethiopian kid in his mouth.
Do you really believe that's an appropriate thing to say about Ethiopians?
It's a joke. If it hurts you, you should go cry in your mothers' laps darling.
Although it may be a joke, when people tell jokes like that, it can cause a lot of harm to the subject of those jokes. When people regularly hear jokes about Ethiopians being dirty or starving, they will start to believe it's true and this leads to thinking they are subhuman. Think about how you would feel if people constantly told insulting jokes about the country you are from.