Troy tells Abed that he's related to Danny Glover. Troy is played by actor Donald Glover and although not related to Danny Glover, it's often assumed.
Jeff says that compared to community college, he's Alan Dershowitz. Alan Dershowitz is a famous attorney who was part of the "Dream Team" that got O.J. Simpson acquitted of murder; he also got Claus von Bülow acquitted of murder and defended Patty Hearst, Jim Bakker, and Mike Tyson. He's also part of the defense team for Harvey Weinstein who - as of 2019 - faces dozens of allegations of rape, sexual harassment, and sexual abuse.
It's revealed that Dean Pelton's first name is Craig.
There's many jokes about British teeth at the expense of Prof. Duncan, however that stereotype was proven to be rather inaccurate. Statistically, Americans have more missing teeth than Brits, and overall access to preventive dentistry is better in the UK. Wealthy and middle class Americans do spend more on cosmetic dentistry though, fuelling the stereotype, especially in Hollywood where almost everyone has a perfect smile.