‘Mouth Breather’
Like yeah I don’t get this one. We all breathe through our mouths (and noses), because we have to. Yet I read this sometimes as it is used like an insult. So what are you saying? You’re insulting someone for doing what billions of other human beings have to do naturally?
That feels like a bit of a jump. I’ve associated “mouth breather” with insults like “slack jawed yokel” or even just “dumb face”. It’s someone who generally looks like they’re not comprehending what’s going on around them and not smart.