Supposedly the word 'naff' derives from the Australian expression 'Nasty as
fuck'. It has two distinct meanings - either as a synonym for
fuck (as in 'naff off, you
oik'), or as a term for something which is shoddy, unfashionable,
kitsch or generally unimpressive.
For whatever reason it is usually associated with posh people, perhaps because Princess Anne once told some Daily Mirror photographers to 'naff off'. In this case it should be pronounced 'narf'.
Ronnie Barker used the word a lot in the classic sitcom 'Porridge', as of course family sitcoms in those days were not allowed to have proper swearing in them, even those set in prison. Nowadays this makes 'Porridge' seem slightly surreal, although it undoubtedly seemed slightly surreal in the 1970s, as people swore just as men then as they do nowadays.