I'm an English major who's anal retentive about his grammar (unless it's for flavor, as in, for example, the next sentence). But I gotta say, (and this took me a long time to learn) leave people alone when they make trivial mistakes. You're just wasting your time, and besides, nobody, including him, cares.
Edit: Added smiley icon so my reply wouldn't be taken as grumpy. :)
Edit: Added smiley icon so my reply wouldn't be taken as grumpy. :)