I remember the days (he says, pulling up a sandbag and giving the lantern a nudge) when the O2 tag was used as a warning to regular ARRSErs that a user had already been identified as a mong and not worth talking to.
Now it seems to be a bit of an AGAI 67 sanction;
'B-T, you've been a very naughty boy and failed the ARRSE service test. Take two weeks with an O2 tag and if you learn to toe the line in that period then we might think of taking it off you.'
The thought police are everywhere my friends, where's my tin-foil hat.