An expression of something very shit.
Usually related to the way someone is feeling.
Person 1 - How you feeling after your night out?
Person 2 - Ohh mate, i feel like gash warmed up in the microwave.

Mate you forgot your keys....
OH GASH WARMED UP IN THE MICROWAVE!!
by Stevie A May 23, 2008
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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.
by sbvodka July 28, 2010
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To step up to someone in a fight.
Yo quit "Gashing up" to me.
by thahib December 21, 2019
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To act like your brave when your really a coward.
Yo you wanna Gash up I'll run up on ya too.
by thahib December 4, 2019
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