adapted from https://eu4cheats.com/command/insult

Your mother was a hamster and your father smells of elderberries!
Judgment day is upon us! The minions of Lucifer walk upon the earth- Oh. No, it is merely the $faction.
Furthermore, I believe that $capital must be destroyed!
When the account of our time is written by future generations, they will look at you with that mix of pity and disgust called compassion.
My last visit to the commode was vastly more enjoyable than dinner with the $faction ambassador.
Oh look. There's some lovely filth over here.
Your blood will make the soil I take from you all the richer.
The $faction know nothing about running a state!
In this great game we play, you are a mere pawn.
In $otherFaction, '$faction' is a word synonymous with manure.
Tales of your misdeeds are told from Tartessus to Nachiketa.
$Faction culture is something of an oxymoron, don't you think?
May your sky be filled with comets.
No map can be a work of art as long as your nation is on it.
What are you going to do, bleed on me?
One day, even $faction merchants will understand bookkeeping.
Your entire line suffers from delusions of adequacy.
It is a dangerous wonder how a heathen such as yourself acquire such a rich and prosperous land. Luckily that will soon be rectified.
You are the scourge of this earth and shall be hanged from your walls for what you've done!
You fight like a cow!
You fight like a dairy farmer!
$playerName's head is as empty as a eunuch's underpants.
l2playnoob!
Git gud.
When our sons look back on today, it will be known that while you may have shaved off our beard, we will remove your arm.
If $playerName fell into a black hole, that would be a misfortune. But if someone dragged $playerHimOrHer out again, that would be a calamity.
$playerName is a proud, popish, presumptuous, profane, pestilent, pernicious prelate and usurper.
Your ruler is an unlawful, unnatural, false, bastardly governor of the Church, the Ordinance of the Devil, petty Pope, anti-Christ, incarnate devil, cozening knave, and prolific liar.
Your walls will crumble before our cannon like sand before the sea.
Your corpse will pave the path of progress, $playerName!
I had another insult prepared for you, but I doubt you would be able to read it.
I suggest you change your uniform trousers to brown.
Not even seppuku could restore your honor.
The dreadful state of your economy is a warning to all would-be rulers.
I hear your people are revolting. You have that in common.
We will impale $playerName on a spike, as we have done with your pathetic armies.
We shall take your lives, and your freedom!
May you succumb to Samsara and live a thousand lives without joy or enlightenment.
Your kingdom is truly worth only a horse.
Our arrows will blot out the sun!
Your misdeeds so far are nothing but a petty sore. Correct them before they become infected beyond the point of help.
If you keep on drinking rum, the world will soon be quit of a very dirty scoundrel!
I once owned a dog that was smarter than you.
I give you a choice. You can be gutted, or decapitated!
It is true, I admit, that $faction is of greater extent than $otherFaction. But you must agree that $otherFaction rules over men, while $faction rules only over forests and mosquitoes.

others:

Die, monster. You don't belong in this world!