ISJ stands for Ian St John, the legendary
ex-
liverpool football player, and the phrase is used to tell someone to "fuck off". The
history behind an ISJ is this: Ian was not the politest person when faced with an autograph request. In his broad accent, and with a hand gesture pointing over his shoulder with his thumb, he used to tell them to "Fuck off and leave me alone laddie". From here on, should anyone ever need to be told to "Fuck off" at
work but without offence being caused to the rest of the office then the 3 letter acronym is used and they are told (often complete with hand gesture) to ISJ