There's apt to be local variation in intensity of prejudice.
Also, throwing acid is extreme behavior, but it's quite possible to be unlucky and happen to be in the presence of someone who is unusually violent.
It makes sense that there would be variation, but saying local variation implies local correlation. Why would that be? Do people feel a need to be racist to about the same degree as their peers?
There's a tradition in England - I don't know how old - of abusing red-headed people. It's a genuine prejudice in England. From this facebook page:
This spread to the US in 2005, when Cartman tried to incite violence against redheads in a South Park episode with "Kick a Ginger Day".
What's interesting is how this meme is spreading in the US: As humor. This meme is promoted by sites like CollegeHumor.com and MyLifeIsAverage.com, which mine it as a source of ironic humor. The Cheezburger Network is pushing ginger-hatred almost as aggressively as they push pedophilia as a fount of humor.
Are humans capable of, collectively, keeping real and humorous/ironic racism separate? No, they are not. What South Park "kicked" off as an ironic commentary on racism is becoming actual racism.
One clue that you're going too far in your ironic humor is when you start finding the real thing funny.
Do humans have an instinctive need to bond over shared prejudices? Is combating racism a game of whack-a-mole, in which society invents new prejudices to replace the ones being taken away?