mouth-breather
n.— «Whatta maroon. Not only does this submoronic mouthbreather send an illegal, obscene message in private email, he posts it here publicly, with a header showing that it was also sent privately.» —“Re: Need help from someone with Win95 expertise” by Lon Stowell Usenet: alt.revenge Jan. 23, 1997. (source: Double-Tongued Dictionary)
Further reading
Understanding the varieties of conversational styles can mean the difference between feeling you’re understood and being insulted. “High-involvement” speakers interrupt or talk along with someone else to signal their enthusiasm...