Many, many of the pre-battle speeches. Some of them use Refuge in Audacity and Vulgar Humor then finishing up the speech with a religious statement. It is just so weird to have a noble warrior say he will sex up the enemies women in one speech and say that he is doing Christ's work in another while calling the French smelly and unwashed using old terms like "knave" like they're candy.
English General: Well hail, slap my thighs and call me for dinner! I see a foe worth the killing and lads beside me who are up to the mark. I can also feel and inspiring speech coming on, so listen to me...
Mongol General: [to his enemy] Struggle if you like, I will take your lands and women, regardless; You will have no rights, once you are my prisoner; Was it your brother I killed? You all look alike to me.
The absolutely ridiculous ways spies sneak into places and the strange ways your assassin can fail. How about putting a venomous snake on the ground of a general's bedroom and having it slither right out of the room or even better, the snake bites the assassin. Or the assassin hiding behind a door and the general opens it so fast, the assassin gets hit in by the door in the nose or, even better, is KILLED by the door while the general runs away screaming. Ever see a spy hide in a bush or haystack and get stabbed by a suspicious guard? Or most ridiculous of all, trying to drop a rock on a calvaryman?
Becoming very trustworthy and getting max happiness with another kingdom by offering ONE florin to them and having them accept a few dozen times (in one turn by using the gift option), then IMMEDIATELY getting attacked by them next turn making it impossible for anyone to ever trust them later. Florin for you thoughts?
Well, almost always. You can kill a princess with assassination (I've done it), you'll just probably need Save Scumming to get lucky enough.
Being offered vassalage by an enemy, despite you being more powerful than them by a wide margin. The epitome of Small Name, Big Ego. Alternatively, the diplomat of an enemy whose empire you've reduced to a single territory offering a ceasefire...in exchange for a huge payout and several of their territories back. It seems like these diplomats are programmed to always bargain as if they're in a position of power.
Having negotiations go sour with a princess from the Holy Roman Empire can have her taunt you.
HRE Princess: Not the first time you've left a fraulein unsatisfied, nein?
Princesses can have high charm even when they gain ugliness traits. It is indeed quite possible to have a maximum charm princess who any foreign prince would love to marry, but whose face has earned her an unfortunate name like "Agnes the Gorgon".
If a General or Family Member marries a Princess with the "Secret Lover" trait he will become known as "The Cuckold." This is made even funnier now that "cuck" has become a go to insult for internet trolls in the years following the games release.
On some occasions, a enemy Prince will give you a mission to kill his father so that he can take power of his almost ruined kingdom. He will inevitably betray you if you succeed. However, many times, his father will be in their faction's last city. You can kill his father as requested and he will laugh at you for doing his bidding at the exact moment his faction falls and he becomes a rebel (unlike the later Rome 2, rebels can reform destroyed factions).