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8.
Any person who is so stupid that they don't have the ability to breathe out of their nose.

A person who cannot cut over a 35 on their ASVAB.

Somebody who's lower lip is so big that it can be caught on a trip wire due to the over breathing through the only orifice they know how to breathe out of.
Mike isn't quite a Glass Licker, however we'll give him the status of Mouth Breather because he got a 25 on his ASVAB.

Josh is a Mouth Breather. His girlfriend, who's been sleeping around with half of the state, has him fooled into believing they will get married.

Josh says he gets 5,000 dollars a month hauling milk... what a mouth breather.
by Randomus August 25, 2006
 
1.
1. literally, someone who lacks enough intelligence that they never learned to breathe through their nose.

2. a really dumb person.
In his latest work, the director has forsaken the indie audience and made something for the mouthbreathers.
by hedgerow September 03, 2003
 
2.
A stupid person who breathes through their mouth, like P Diddy.
P Diddy is a mouth breather
by ===0) December 29, 2004
 
3.
1. Someone who is incapable of breathing through their nose

2. Someone stupid who is unaware that their mouth is gaping open, often taking in gallons of air and spewing their own dry, bacteria rotten maw into your clean air in your vicinity.
Never let a mouth-breather speak to you very close, or you might regret it.
by Randall Wynn April 06, 2008
 
4.
A person who breathes through their mouth, thus having their mouth hang open. Their mouth can be anywhere from barely open, to gaping, and usually the more open it is, the more idiotic, and unintelligent they look. Mouth Breathers may or may not be intelligent, however, due to the fact that they don't realize their mouth is gaping, they just look like a moron, who may drool at any moment, but is deffinately sucking in as much air as possible.

Mouth breathers tend to be people who are bored, zoning out, very focused on something, someone with huge lips, or someone who isn't smart enough to realize their mouth is hanging open, catching flys. All tend to appear as the latter.

People who are sick and can't actually breathe through their noses do not count.
Katie: "I was sitting in class, and I looked over at Fred, who was staring dead eyed at the board with his mouth hanging open, like an idiot"

Rachel: "Ew, what a Mouth Breather"
by JelloLove September 15, 2010
 
5.
A person of inferior intellect that lacks the faculties to recognize he is breathing heavily through his drooping open mouth; one who watches Fox News and Nascar with religious zeal.
Donnie shops at Evil-Mart like all the other mouth breathers.
by Joe Flood September 04, 2007
 
6.
A nearly wiped out ethnic group of humans who breath very noisily through the mouth only. Major causes of death are from suffocation while: giving blow jobs, eating, or attempting to breathe from the nose.
1. Alex almost suffocated yesterday while eating; he must be a Mouth Breather.
2. Sadly, Alexis suffocated while giving Mr. Andryszak a blow job. She was the last female Mouth Breather.
by Douglas Page February 22, 2005
 
7.
Adj: - derogative term - Someone of a lower (or no) class – Usually found in large packs in city centres – can be of any age (although motherhood stats at 14) – standard attire – Tracksuit bottoms – fake Burberry caps – jewellery from Elisabeth Duke of Argos. Derived from the fact they breathe through there mouths.
1; the mouth breathers stood in the dole queue.
2; the mouth breathers considered Primark to be an expensive shop.
3; the mouth breathers were unfamiliar with the concept of books or chewing with ones mouth closed.
by Andy The Great July 21, 2003