Naff

As used elsewhere lower down this page, the word "naff" is (I am fairly sure) peculiarly British. It seems to be used in two slightly different ways:

i) as a replacement for a more vulgar expletive - as in when someone is told to "naff off" or when something is "naffing awful". However, I'm sure that there's no stand-alone verb "to naff".

ii) as an adjective meaning tasteless, worthless or just generally bad. Someone can be wearing a "naff" shirt, or can go to a "naff" party.

Origins, anyone? I'm at a loss.