1. Someone who is really dumb
2. A person who doesn't/can't breathe through their nose
by A-Claire February 21, 2017
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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 4, 2003
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The word Eleven in Stranger Things uses to call someone a Bullshitter.
'Mouthbreather'
by Strangest Things December 29, 2018
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someone who is ignorant to the social courtesies of public movement. consequently, they stifle the mobility of thinking humans by becoming an obstacle which must be negotiated. they can be identified by their despondent facial expressions and wide-open mouths .
Man, I wish these mouthbreathers would get out of my f**king way! I hate people who don't pay attention to where they are going.
by dee eye zee December 21, 2008
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A person of low intellect who is incapable of critical thinking. A mouthbreather watches Fox News religiously and believes everything they hear there as well as anything on the Internet that validates their ignorance.
Donald Trump appeals to every mouthbreather in the country because he is as ignorant and unimaginative as they are.
by SheckyGrl November 13, 2015
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1) Person incapable of their own thought, who when faced with a decision, or when asked about personal opinion on something opens up her or his mouth in shock and astonishment that there is such thing as personal opinion. With mouthbreathers it happens constantly due to damage caused by upbringing by helicopter parents, or other emotionally damaging authoritarian or social influences. Can be spotted at every step of social and economic status ladders.

2) A reason why normal people invented law of the land ( equivalent of pinning a note that states "anyone who will touch my coffee cup will get their car keyed" ) and lawyers to herd those idiots away from harming normal families.

3) Equivalent to an alarmist or a zombie - AVOID AT ALL COST - prolonged exposure might lead to compromise of inner emotional barriers and contamination of own soul with emotional AIDS. If you really want to help such person you can only put some objects in their way in hope it will trigger aha moment in them, so they will start slowly doing stuff for themselves - pretty much the same deal as when handling alcoholics. When engaging personally with help there is high chance of them making their mess your business, continuing their crazy of not doing anything for themselves.

4) Private Pyle from Full Metal Jacket after emotional fuckery by Gunnery Sgt Hartman
me (at university): So mr advisor, is what I wrote in thesis valid and does it have your okay stamp?
advisor: No, you gotta change thingie A to B
me: umm... but why? the whole world is doing A. B is kinda retarded way (provided metric shit ton of references)
advisor: No, you gotta change A to B
me: (oh fuck... im dealing with a mouthbreather here...) okaaaay, so can i post that on my blog so the whole world will know you are in favor of B?
advisor: (says nothing)
me: so, can I now assume that A stays and all is kosher?
advisor: *okay*
me: THANK YOU! (sigh... finally)

(true story)
by Spaceship Earth Astronaut November 16, 2012
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