The phrase "were foul-mouthed" can be replaced with a plethora of synonyms, each with their own degree of intensity. Some options include using obscenities, cursing, swearing, or using vulgar language. These words convey a clear sense of using offensive language. Other milder synonyms may include impolite language, disrespectful language, harsh language, or abrasive language. These phrases acknowledge that the language used is rude and may be hurtful, but do not necessarily imply the use of explicit language. Ultimately, the choice of synonym depends on the context and desired level of emphasis.