Means that they are good friends, almost suggesting that others are excluded.
Not a phrase to worry about or try to use. Very out of date.
Yes, I have seen "The IT Crowd". It is what can be called a show with "in jokes" - jokes understood by those who watch it. Not as clever as it used to be.
If it was Moss who said this, that is entirely in character for him - nerdy and out of touch with current slang.
If you have a question about the English language and would like to ask one of our many English teachers and language experts, please click the button below to let us know: