When a person gets bored of one persons vagina so has to swap from fanny to fanny. Also if a person does not get action from his girlfriend or only once or twice a week so finds other girls so he can get gash all week.
Joe: Woww i've got a proper gash mash-up this week lillie on monday then ellie tuesday then my girlfriends sleeping over wednesday but friday i think i will see Georgie.
Jack: Ahh cant be arsed my girlfriends fanny is to tight i get bored might as well go fuck Georgie.
Put a banana in a sock, mash it up and put it in microwave for 20seconds. When done put it over your penis and start masturbating.
(20 secs only so you dont burn your knob)
I'm going yo get home and have a mashed up monkey