I think it's funny that people get so angry when someone corrects their grammar or spelling. It's not our fault you're an illiterate idiot.
Why do you find that funny?
They get so defensive when I tell them that they spelled something wrong.
It is not constructive to demean people because they aren't very good at spelling or grammar. It would be more helpful to teach them how to spell properly in a kind way.
I can only teach them in my way.
If your way of teaching involved calling them rude names or saying that they're illiterate, then your way of teaching isn't helpful. You should be kind when you let someone know that they've made a spelling or grammar mistake.