It is important to have a robust vocabulary to avoid repetition in your writing. Synonyms for the phrase "are foulmouthed" can include uncouth, vulgar, profane, crude, offensive, inappropriate, abusive, and coarse. These words can be used interchangeably to describe people who have a tendency to use vulgar language in their speech. By incorporating these synonyms, you can add variety to your writing and make it more engaging for your readers. Remember to always choose the word that best fits the context of your writing and be mindful of your audience.