Mouth Breather

Mouth breather is an insult used across mainstream English to call someone dim, dull, or clueless. The image behind it is a person who breathes loudly through an open mouth and appears slack-jawed and unthinking, and dictionaries such as Cambridge define it simply as "a stupid person." It is not a term rooted in LGBTQ+ culture and carries no established queer or sexual meaning, so any claim that it refers to a specific sexual role is unsupported. Because the phrase also describes a real medical breathing pattern, some clinicians and advocates note that using it as a slur can mock people with genuine nasal or airway conditions.