Personally, I'm an easy-going pedant. I can spot mistakes, and will point them out if amusing enough, but they don't bother me, which I guess is why I never wanted to be a teacher.*
Plus, of course, it's easy to get all hoity-toity about poor grammar and spelling, but scientific/technical stuff baffles me, and whilst I do reasonably well with basic arithmetic, algebra is a closed book, geometry leaves me cold, and my graphs at school were a combination of guesswork and looking over someone's shoulder and copying what they'd done.
*Possibly my favourite was a newspaper misprint, published in Private Eye many years ago. It was a report of a cycle race, in which an injured competitor bravely carried on. According to the paper 'Though he did his best, he was clearly in pain, and feeling every bum on the road'.