A subspecies of Homo-sapiens known for their lack of any intelligence whatsoever. Their young are raised entirely on a diet of Ribena and Chicken Nuggets, whilst the adults have no interests other than Stella Artois and ITV2.
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.
Someone who's been in too many fistfights and thus has had the ability to breathe through the nose beaten out of him. The usual implication is that the ability to use the brain has also been beaten out of him.
My bookie sent a mouth breather to collect for him, but when the goon tried to get me to head to the ATM with him I escaped for the moment by saying his shoe was untied.