Dogbert:"A disturbing number of [the readers] have requested the return of Loud Howard. Loud Howard is neither funny nor insightful. He is simply loud. It's a wonder why anyone would want more of this guy.
Loud Howard:"THEY LOVE ME!"
It should be noted that after his first (and for the longest time, only) appearance in the strip Loud Howard was made a supporting character in the cartoon (shouting the obvious works a lot better as a gag in animation) in order to expand the cast. Had Adams not done this it is doubtful the masses would've demanded his return to the strip.
Catbert, notable for being the only character the fans named (see Sure Why Not below).
There’s also one about a plane belonging to their Pointed Haired Boss crashing. Dilbert and Wally debate on rather do should they stay to celebrate with Asok, mourn, or leave early. Bear in mind, this was released on September 11, 1997… you can guess what happened exactly 4 years later.
Genius Bonus: The fable that the Pointy-Haired Boss relates in this strip is traditionally used to explain the Scrum software development methodology. If you're not familiar with Scrum, the strip is still very funny, but if you are, it's clear that the PHB thinks himself clever for using an analogy that he read somewhere else and probably doesn't understand.
One Sunday strip featured a security guard who secretly raided the employees' hidden snack stashes during the night. Whoever did the colors made him black, which lead to people accusing Adams of this (in the anniversary book, he explains the whole thing while wryly observing that they chose a poor time to diversify the cast).
The TV series:
Crosses the Line Twice: Alice marries a death-row inmate and immediately stuffs the gag into his mouth herself before he's executed. It's much more horrifying than it sounds.
Everyone Is Jesus in Purgatory: Parodied in a (nun) art expert who insists everything is about barely suppressed sexual urges. It's obvious that she's projecting so hard that they could use her for powerpoint presentations.
Magnificent Bastard: Dogbert, whose "religious belief" is "that everyone exists for the sole purpose of entertaining me." On one episode, he sets up a carnival booth where you "knock a street urchin off a beam with a baseball and win a toy." In another, he convinces Congress to abandon all holidays in favor of National Dogbert Day (The traditional Dogbert Day feast: the bald eagle. He wanted something special) for the sole purpose of being annoying. (The same reason he invented Secretary's Day.)
The aptly named Bob Bastard, the caped and hooded company tester on a quest to crush the hopes and dreams of engineers.
Dilbert: I'm sorry Alice, but he's the embodiment of all that's horrid and loathsome in this world.
Alice: Just because it's written on a bathroom wall doesn't mean it's true.