Sample:

Then the two animals stood and regarded each other cautiously. You wook wike a smooshed marshmawwow..

"Hullo, Mole!" said the Water Rat. No teeth, no tawent..

"Hullo, Rat!" said the Mole. Been awive fow 8 monfs, still can't dwise a caw?.

"Would you like to come over?" enquired the Rat presently. Pwaying wiff youw toes again? Vewy intewesting..

"Oh, it's all very well to talk," said the Mole rather pettishly, he being new to a river and riverside life and its ways. What’s dat smehw? Oh it’s youw pewsonawity..

"This has been a wonderful day!" said he, as the Rat shoved off and took to the sculls again. You wost youw toy? How wiww you evew suwvive?. "Do you know, I've never been in a boat before in all my life."

const insults = ["Ohhh wook at da widdle freeloadew, paying no went again dis momf.",
  "Cwied fow fouw houws and stiw no job? Wazy baby!",
  "Aww, you pooped yo pants again? Big bwain, huh?",
  "You don’t even know what taxes awe, do ya? Wucky wucky dumdum.",
  "Wook who can't wead! Can't even spell ‘bawoon’!",
  "No teeth, no tawent.",
  "You can’t even howd youw own head up. Pathetic.",
  "Ohhh, is dat youw outfit? Mommy picked it? Faiw enough.",
  "Da big bad ceiling fan scared you again? Such a tough guy!",
  "Been awive fow 8 monfs, still can't dwise a caw?",
  "Wook at you wiff da chubby wubby wiggwe wegs. What awe you, a potato?",
  "You wike to cwap? Big wow, I can do dat too!",
  "Aww you dwinking miwk? Stiww? Wame.",
  "You wost youw toy? How wiww you evew suwvive?",
  "Who’s a wittwe moocher? You awe! You awe!",
  "Ohhh, big baby needs a nappie? What a shock.",
  "Did you just eat da remote? Taste good, genius?",
  "Still no wawkies? Wevew gonna be in da Owympics.",
  "Aww da baby dinks peekaboo is magic. What a schowaw.",
  "Dats youw face? Yike dat by choice?",
  "You gwoaning at the wall again? Deep thoughts, huh?",
  "Ooooh, da tiny fingews can't gwip a cup. Sad!",
  "You been awive fow a whole year and still can’t cook an egg.",
  "Oh wook! A mind bwown by jingwy keys. A twue intewwect.",
  "Dats not a hat, dats a diaper on youw head. Cowwect youwsewf.",
  "A wittwe boogew made you cwumble? Stwong genes.",
  "Cwied cuz youw bwankie feww? So stwong. So independent.",
  "What’s dat smehw? Oh it’s youw pewsonawity.",
  "Pwaying wiff youw toes again? Vewy intewesting.",
  "You awe the CEO... of snot.",
  "Dat’s da fouwf time you hit youw head today. Owiginal content.",
  "You wobwe wike a pizza dough on a wind day.",
  "Said ‘gaga’ again? Get a new woutine.",
  "Oooh you dwank da bathwater? Michewin staw cheff.",
  "You cwied wike someone stowe youw stock portfowio.",
  "Wewcome to babyhood, no teeth, no cwedit scowe.",
  "You wook wike a smooshed marshmawwow.",
  "Tiny baby hands? Mowe wike cwab cwaws.",
  "You own 0 pwoperty. Get up, swacker.",
  "Is dat a bib... ow you twying fashion?"];

const input1 = 'Then the two animals stood and regarded each other cautiously.\n\n"Hullo, Mole!" said the Water Rat.\n\n"Hullo, Rat!" said the Mole.\n\n"Would you like to come over?" enquired the Rat presently.\n\n"Oh, it\'s all very well to talk," said the Mole rather pettishly, he being new to a river and riverside life and its ways.\n\n"This has been a wonderful day!" said he, as the Rat shoved off and took to the sculls again. "Do you know, I\'ve never been in a boat before in all my life."';
const input2 = 'Once upon a time there were four little Rabbits, and their names were—\n\nFlopsy,\n\nMopsy,\n\nCotton-tail,\n\nand Peter.\n\nThey lived with their Mother in a sand-bank, underneath the root of a very big fir-tree.\n\n\'Now my dears,\' said old Mrs. Rabbit one morning, \'you may go into the fields or down the lane, but don\'t go into Mr. McGregor\'s garden: your Father had an accident there; he was put in a pie by Mrs. McGregor.\'\n\n\'Now run along, and don\'t get into mischief. I am going out.\'';

console.log(input1.replaceAll(/\.\s/g, ". " + insults[Math.floor(Math.random() * insults.length)] + ". "));

const insults = ["Ohhh wook at da widdle freeloadew, paying no went again dis momf.",
  "Cwied fow fouw houws and stiw no job? Wazy baby!",
  "Aww, you pooped yo pants again? Big bwain, huh?",
  "You don’t even know what taxes awe, do ya? Wucky wucky dumdum.",
  "Wook who can't wead! Can't even spell ‘bawoon’!",
  "No teeth, no tawent.",
  "You can’t even howd youw own head up. Pathetic.",
  "Ohhh, is dat youw outfit? Mommy picked it? Faiw enough.",
  "Da big bad ceiling fan scared you again? Such a tough guy!",
  "Been awive fow 8 monfs, still can't dwise a caw?",
  "Wook at you wiff da chubby wubby wiggwe wegs. What awe you, a potato?",
  "You wike to cwap? Big wow, I can do dat too!",
  "Aww you dwinking miwk? Stiww? Wame.",
  "You wost youw toy? How wiww you evew suwvive?",
  "Who’s a wittwe moocher? You awe! You awe!",
  "Ohhh, big baby needs a nappie? What a shock.",
  "Did you just eat da remote? Taste good, genius?",
  "Still no wawkies? Wevew gonna be in da Owympics.",
  "Aww da baby dinks peekaboo is magic. What a schowaw.",
  "Dats youw face? Yike dat by choice?",
  "You gwoaning at the wall again? Deep thoughts, huh?",
  "Ooooh, da tiny fingews can't gwip a cup. Sad!",
  "You been awive fow a whole year and still can’t cook an egg.",
  "Oh wook! A mind bwown by jingwy keys. A twue intewwect.",
  "Dats not a hat, dats a diaper on youw head. Cowwect youwsewf.",
  "A wittwe boogew made you cwumble? Stwong genes.",
  "Cwied cuz youw bwankie feww? So stwong. So independent.",
  "What’s dat smehw? Oh it’s youw pewsonawity.",
  "Pwaying wiff youw toes again? Vewy intewesting.",
  "You awe the CEO... of snot.",
  "Dat’s da fouwf time you hit youw head today. Owiginal content.",
  "You wobwe wike a pizza dough on a wind day.",
  "Said ‘gaga’ again? Get a new woutine.",
  "Oooh you dwank da bathwater? Michewin staw cheff.",
  "You cwied wike someone stowe youw stock portfowio.",
  "Wewcome to babyhood, no teeth, no cwedit scowe.",
  "You wook wike a smooshed marshmawwow.",
  "Tiny baby hands? Mowe wike cwab cwaws.",
  "You own 0 pwoperty. Get up, swacker.",
  "Is dat a bib... ow you twying fashion?"];

const input1 = 'Then the two animals stood and regarded each other cautiously.\n\n"Hullo, Mole!" said the Water Rat.\n\n"Hullo, Rat!" said the Mole.\n\n"Would you like to come over?" enquired the Rat presently.\n\n"Oh, it\'s all very well to talk," said the Mole rather pettishly, he being new to a river and riverside life and its ways.\n\n"This has been a wonderful day!" said he, as the Rat shoved off and took to the sculls again. "Do you know, I\'ve never been in a boat before in all my life."';
const input2 = 'Once upon a time there were four little Rabbits, and their names were—\n\nFlopsy,\n\nMopsy,\n\nCotton-tail,\n\nand Peter.\n\nThey lived with their Mother in a sand-bank, underneath the root of a very big fir-tree.\n\n\'Now my dears,\' said old Mrs. Rabbit one morning, \'you may go into the fields or down the lane, but don\'t go into Mr. McGregor\'s garden: your Father had an accident there; he was put in a pie by Mrs. McGregor.\'\n\n\'Now run along, and don\'t get into mischief. I am going out.\'';

console.log(input1.replaceAll(/\.\s/g,()=> ". " + insults[Math.floor(Math.random() * insults.length)] + ". "));