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.
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.
Rachel: "Ew, what a Mouth Breather"
2. Sadly, Alexis suffocated while giving Mr. Andryszak a blow job. She was the last female Mouth Breather.
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.