Looks like a police officer was not following the advice of the article detailed below.

Some details:

A police constable has been sacked for posting offensive messages about a colleague on Facebook and harassing a female colleague.

The 35-year-old Met officer, who was based in Islington, referred to another officer as a "grass" and a "liar" on the social networking site last year.

See Metropolitan Police officer sacked over Facebook posts (BBC News) for more details.