I would make sure my grammar was spot on if I was writing a paper for school, in a job interview or making a speech. I'm not. I'm having a conversation and I don't need to be proper. As long as my point is understood without any follow-up questions, my communication is obviously fine.
I notice most of the people who do this are strangers or people I do not know well. That is even more reason I consider them to be smug, irritating and condescending. Also, it ruins really good stories.
How does everyone else feel about this topic?
What do you think of the people who do this?
Do you find people who correct grammar to be mainly strangers or people you know well?
If you are a grammar corrector, why do you do it?