Green’s Dictionary of Slang

female masturbation; thus gusset typist, a woman who masturbates.

1997		Roger’s Profanisaurus in Viz 87 Dec. n.p.: gusset typist euph. A woman who masturbates.
2003		record review at www.brainwashed.com 🌐 Side B ends with the hyper-sexualized ‘Gusset Typing,’ in which a mutated woman’s voice describes her masturbation and orgasm in intimate, anatomical detail.
2005		posting at FemaleFirst.co.uk 🌐 Besides, how will one ever get anything done if you spend your life gusset typing?