mashing up a girl's dinner Share definition Flag To perform the act of anal sex on a woman. To fuck a girl in the ass. Last night i was mashing up a girl's dinner and i got shit on my dick! mashing up a girl's dinner by patyouth711 July 18, 2009 0 0 Get merch Get the mashing up a girl's dinner mug. Buy Now — $32.95 See more merch