These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
The reason he doesn't do "Klan Cookout" or "Perfect Woman" live anymore. He's said that he worries about the latter being used to make fun of a real-life deaf girl.
Genius Bonus: "What's domain, domain range? / A kid with too much in his pants". In math, domain is expressed by x, while range is expressed by y—the joke here being that said person is "XXY", which is the chromosomal makeup for a hermaphrodite.
Growing the Beard: Seems to have happened around the time of Words Words Words. He's expressed embarrassment and dislike of much of his work prior to that period, which was more based around shock value for the sake of shock value rather than making a satirical point.
Hilarious in Hindsight: In Welcome to YouTube, he says that "most of the best YouTubers are either Asian or they're gay, so there's an untapped YouTube celebrity and his name is George Takei." While he's not so much specifically a YouTube celebrity, but since the song's debut, Takei has gained a huge internet following.