The phrase "are foul-mouthed" is often used to describe someone who frequently uses offensive language. However, there are many synonyms that can convey this same message in a different way. Some alternative phrases might include "have a dirty mouth," "use vulgar language," "swear excessively," or "employ foul language." Additionally, more colloquial synonyms might include "cuss like a sailor," "drill sergeant language," or "swear like a truck driver." Regardless of the chosen synonym, it's important to remember that using this kind of language can be disrespectful and inappropriate in many situations, so it's best to use it sparingly, if at all.