| The colorful pseudoscience|
|Hating thy neighbour|
|Divide and conquer|
Racist "jokes" reveal a person's underlying feelings about a given race under the defense of being able to deny the racism as "just a joke.". They reduce entire races of people to a punchline and contribute very real racial discrimination. Many neckbeards use racist jokes as a way of being edgy contrarians and insist that they can separate joke from fact. The reality is that they can't see a group of people as both competent and a punchline. Even if they can, their jokes contribute real racism by the people who read them and reinforce the beliefs of actual racists. Every racist joke takes all of the discrimination and persecution that the target race has suffered and uses it as a source of entertainment.
Racist and other tasteless jokes are a staple of websites like 4chan, 8chan, Encyclopaedia Dramatica and similar. A lot of the users on those sites are only posting them "for the lulz" as an anti-social way of upsetting people and watching their reactions in amusement. Plenty of readers assume that these jokes are completely in jest when a (presumably) high amount of posters are serious in expressing their views on blacks and other races, though it's often hard or impossible to tell.
Racist jokes can be ok when they come from a member of a race that they make fun of with the right rhetoric behind them. These jokes can still be harmful because they can become memetic or people outside the target race who don't understand the joke can have their own racism reinforced.