Eric the Red
Team HuskerBoard
Barry Leiba, a technical researcher at IBM and author of the delightful blog "Staring At Empty Pages," said there are "exactly four" situations where it's all right to correct someone's grammar: (1) when you're an English teacher correcting a student, (2) when you're coaching a nonnative speaker who's asked for help, (3) when someone else has asked for coaching, or (4) when someone puts the equivalent of a "kick me" sign on her back.