Green’s Dictionary of Slang

to break wind.

1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: guff v. To fart; let off.
2006		D. Mitchell Black Swan Green 368: Its lid’s so tight it guffs when you open it.
2016		Times 19 Aug. 🌐 You wanna show some darts, love. That’s a serious game. Get Eric Bristow up to the oche. Oi-oi! Has someone just guffed?