"A milkmaid […] I don't know that I could wed one of them even under the best of conditions. People might snicker that she was the best I could do." (3.73)
Prince Humperdinck doesn't like the idea of marrying a milkmaid when Count Rugen makes the suggestion… but he changes his tune pretty quickly when he first sees how beautiful Buttercup is.
"We do not walk among commoners unless it is unavoidable." (5.10)
Being a commoner herself, Buttercup doesn't mind walking among all the people who have come out to see her. But Humperdinck will avoid this kind of contact at all costs. On top of the fact that he's been raised separately from the commoners, the guy's also a jerk who has no interest in interacting with the people he rules over.
There was no doubting her sincerity. Or power. Or capability for vengeance. She stared imperiously across the Brute Squad. (8.177)
Buttercup has never really come to grips with her status as a princess in this book. But when push comes to shove, she's able to step up like a queen and order a bunch of guards to do exactly as she says.
"Your father is dying." (2.21)
When Count Rugen first tells Humperdinck that his father is dying, Humperdinck's first reaction isn't sadness. He actually feels annoyed, since with his father out of the picture, he's going to have to get married and produce an heir for the kingdom.
"That would certainly be a perfect match politically." (3.16)
One of the first suggestions for Humperdinck's new bride is a nice, pretty girl from the neighboring country of Guilder. Only later on, though, does Humperdinck find out that this woman is bald. Yes, she's a princess and all that—but Humperdinck just can't stand the thought of having a bald wife. He might be upper class, but this guy is classless.
Dinner was held in the Great Hall of Lotharon's castle. Ordinarily, they would all have supped in the dining room, but, for an event of this importance, that place was simply too small. (3.37)
The big wigs of Florin know how to throw a party, especially when it's time to show off all their fancy dining rooms. After all, you need to make a big impression when you're royalty. You can't be sitting on mountains of gold and not splurge a little on meals now and then.
"I do not give you permission to move. You stay right exactly where you are or risk my wrath, which, I must tell you in advance, is considerable." (5.298)
Count Rugen is a nobleman, and he's not going to stand by and let a silly commoner like Domingo Montoya disrespect him, so he orders Domingo to stay exactly where he is when Domingo starts to move away. And it's a good idea for Domingo to do as he says, since we find out later just how bad the Count's temper can be.
"You're a peasant and a fool and I want my sword." (5.349)
For the second time, Domingo Montoya disrespects Count Rugen. Except this time, Rugen won't let him get away with it. This is the scene that actually ends with Rugen murdering Domingo and thus creating the revenge machine that is Inigo Montoya.
"So I shall help you as you go through life, by leaving you with a reminder that bad manners are to be avoided." (5.374)
Count Rugen understands why little Inigo Montoya would want to kill him. Then again, he can't let a peasant child get away with calling him a coward and challenging him to a duel, so he gives Inigo two scars to remember him by.
It turned out, because of the King's health, to be both easy and sad. For with fifty-five days to go, Lotharon began to weaken terribly. (6.72)
Poor King Lotharon doesn't really have much of a role in this book other than being sick and constantly on the verge of death. This means that at any moment, Prince Humperdinck could become king. The funny thing is that the guy could do without all that power and responsibility, because all he wants to do is hang out in his Zoo of Death.