That said: Imagine you're Nigerian. Every time this comes up on the web, someone cracks a joke about 419 scams. For this person they maybe make a joke like that say, once a year. No big deal, they're not racist or anything. But Nigerians are vastly outnumbered by people that aren't Nigerian (obviously), so if each of these people makes a once-in-a-blue-moon joke when you mention that you're Nigerian, that means for you it happens every. Damn. Time.
I imagine that gets pretty old.