Somone or something be violently stepped upon by heavy persons or creatures is called the hippo stomp. This is especially true when done with vigor and malice.
Man, those bikers really gave those punks the hippo stomp!
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