Ear Worm - "Iiiii'm gonna sit at the welcome taaaable..." from the cult episodes.
Family-Unfriendly Aesop - parodied in every episode. "I don't have to join the debate team to get people to pay attention to me, I just need to starve myself to the brink of death!" "Drugs are for losers. Unless you use them to win. In that case, drugs are for winners!"
A gif of Noblet removing his glasses while shaking his head in disapproval is a popular reaction image on forums and Image Boards.
Nightmare Fuel: the expression on the face of the shoe salesman as he asks Melissa to step into the back with him, calling her the name of the woman he is implied to have murdered and buried under his shoe store