1. slang A person who uses obscenities, vulgarities, or profanities in their speech. Used especially in reference to a child or as a childish rebuke to an adult. Hey, you little sewer mouth! If I hear you speaking like that around your grandmother again, you're going to be grounded for a week!
2. slang The use of such foul language. Well, there's no need for the sewer mouth, Rick. You could have just said "no" like a civilized person.
n. someone who uses vile language constantly. (Also a rude term of address.) If you’re going to be a sewermouth, I wish you would leave.