Green’s Dictionary of Slang

naff v.

In phrases

naffed off (adj.) [euph. for fucked off under fucked adj.¹ ]

fed up, annoyed.

2004

Guardian G2 12 Mar. 13: We’re naffed off with obstetricians telling us it will be fine when it often isn’t.

naff up (v.) [euph. for fuck up v.]

to make a mess, to blunder.

2001

Gandermonium Archives 🌐 Despite the good approach play, we then proceed to naff up a few good chances.

In exclamations

naff off! [euph. for fuck off! excl.]

go away!

1959		K. Waterhouse Billy Liar (1962) 36: Naff off, Stamp, for Christ sake!
1986		R.G. Barrett Godson 57: ‘I told him to naff off’.
1987		V. Blackman [bk title] Naff Off! Confessions of a Fleet Street Photographer.
1991		Age (Melbourne) 7 Dec. 130/5: The Princess Royal telling an irritating photographer to ‘naff off’.
1999		Indep. Rev. 5 Oct. 5: And next, ‘Naff off, mate.’.
2013		C. Matthews More to Life Than This [ebook] Sonia waved back enthusiastically, while saying, 'Naff off, naff off, naff off,' under her breath.