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1.
a big fannyd bitch thats been cocked more times than john waynes gun
i tied a plank to my arse coz wen i stuck my cock in, i nearly fell in coz she had a fanny like a hippos yawn
by finno lee January 27, 2006
 
2.
a simile for a particularly large vagina, named so because it resembles a hippo yawning. minus the big teeth a hippo possesses of course. that would just be weird.

a hippo's yawn can usually be found attached to a slosher or perhaps a lady that has given birth to twins with heads like south park's mr mackey.
trevor : how'd it go with that slag last night then?
pete : mate, she had a minge like a hippo's yawn
trevor : that bad huh?
pete : seriously, it was like stirring a bucket of wallpaper paste with a pencil
by MrCasual January 06, 2011