A small but vocal subculture has emerged on Twitter of grammar and taste vigilantes who spend their time policing other people’s tweets — celebrities and nobodies alike. These are people who build their own algorithms to sniff out Twitter messages that are distasteful to them — tweets with typos or flawed grammar, or written in ALLCAPS — and then send scolding notes to the offenders. They see themselves as the guardians of an emerging behavior code: Twetiquette.

On the Twitter Patrol - NYTimes.com