"Run off at the mouth" is a colloquial phrase that refers to someone talking excessively or making unnecessary comments. There are various synonyms that can be used in place of this phrase to convey the same meaning. For instance, one can use the term "blabbermouth" to describe someone who is excessively talkative. Other synonyms include "yammer," "jabber," "chatterbox," "gab," and "prattle." Additionally, one can use phrases like "talk too much," "ramble on," "go on and on," or "spout off" to demonstrate repetitive and unnecessary speech. However, regardless of the word choice, all of these synonyms can be used interchangeably to describe someone who talks too much or is engaged in unwarranted conversations.