Tons and tons of the descriptions all over the place. Putting your mouse over pretty much anything that stands out is bound to elicit at least a chuckle.
Even one of the wikis has one moment. In the Achievements page, it details what is referenced by each achievement's name. And then you get to "I Can't Believe That Worked!"note Beat Dredmor while having picked your skills with the Randomize button:
Explanation: Well, do you?
A lot of the announcer quotes:
"You need food, baldy! Uh, what? 'Badly'? Oh, right!"
In the .txt files for monsters, skills and items, one can find there's quite a few debug notes that were left in, many of them worth a chuckle. Particularly many of the "What the everloving hell is this spell doing!?"-style comments.