Green’s Dictionary of Slang

spaff v.

1. to ejaculate.

1994		rec.sport.basketball.college 14 June 🌐 The guy is renowned throughout New Mexico city and the state for his enormus slong [sic] and the spaffing potential of his long john sliver [sic] [...] It was like a baby's arm holding an apple.
1999		Roger’s Profanisaurus in Viz 98 Oct. 26: spaff v. To spoff (qv) or spod (qv). ‘No, no, no, Gunter! Be professional. Spaff on the chest, not in the pussy.’ (from an unidentified porn film c. 1980).

2. in fig. use, to throw away.

2019

M. Hyde Guardian 16 Jan. 🌐 [T]he referendum vote was problematically close anyway, and then you totally spaffed your majority. Like, you literally have no majority.

In derivatives

spaffy (adj.)

affected, ‘wanky’.

2020

I. Dunt on Twitter 4 Nov. 🌐 I maintain my position that semi-colons are posh and spaffy.