I'm sick of proofreading things for my friends. I'm gonna lie when they ask next time.
Why don't you want to help them?
They're always inaccurate and it never changes.
Proofreading things is the only way to spot and fix errors in writing. Instead of being upset, you should see it as a good thing that your friend's are trying to improve their work.
I see it as them being lazy and passing the work to me. I'm not proofreading their next projects.
Then just be honest with them and tell them you're tired of being their editor.