In "Curses", Townsville was under attack, by The Potty Mouth Monster. The Potty Mouth Monster roamed the streets of Townsville, spewing out a slew of shocking profanities, that seemed to have been leaving a stronger impact on Townsville, than the damage he was causing to the buildings. Everyone in Townsville was totally appalled by his language, as their delicate ears couldn't take the horrible dialogue. The Potty Mouth Monster's "profanities", were really just nonsensical gibberish ramblings, used as a stand-in for swearing, since they couldn't use actual swear words in a children's show. However, other instances of swearing in the show were presented as real words, but in-universe sounds were providing censorship.
The Powerpuff Girls came to the rescue, but instead of attacking The Potty Mouth Monster, they became intrigued by the kind of language he was using, and they stopped to ask him about these new words. The Powerpuff Girls had a profane conversation with The Potty Mouth Monster, where he started teaching them new cuss words and they kept repeating them. Everyone in Townsville was appalled by the language, as the dialogue was getting too heavy, even for the gang members, criminals, and thugs.
The Potty Mouth Monster was holding up traffic, which Professor Utonium happened to be driving in. He saw what was going on, but didn't heart any of it, until got out of his car to admire his three little girls, saving the day. As soon as he heard them cussing, he was horrified by their language, and he angrily called them down, to give them a talking to about what they've been saying. However, Bubbles mentioned that she learned the word from him, after hearing him scream it, when burning his hand on the stove, and afterwards, she introduced it to her sisters. This made things very awkward for The Professor, as the rest of the citizens of Townsville gave him dirty looks for what he did. Professor Utonium told the girls that he should not have used that word, and none of the words The Potty Mouth monster is teaching them are good either.
The Powerpuff Girls went back to The Potty Mouth Monster and taught him a lesson about swearing. Blossom picked up a truck of unpackaged soap and dumped it all in The Potty Mouth Monster's mouth. She then told him to go stand in a corner-shaped building and think about what he did.
The Potty Mouth Monster is a giant white dinosaur-like creature with a porcelain toilet for a head. The monster's mouth is the lid of the toilet, opening and closing. He has a bunch of spiky blue teeth on the inside of his lid and he has yellow eyes. His arms are blue and he has three claw nails on each hand. The same goes for his legs and toenails. His belly is teal and aquamarine. He has a strip of toilet paper as a tail.
The Potty Mouth Monster is a very disgusting, unpleasant monster to be around, who lacks charm and class, and is most infamous for his overuse of foul language. Everything he says is crude and profane, and his language comes across as extremely shocking and offensive, to everyone who hears it.