"Squishy" is a name to describe the hidden bitch within.
The name "Hippo" comes from the hiding characteristic of a Hippopotamus, being able to hide their anger by being calm and/or lazy.
Squishy Hippo:... OK, Gurl. Love ya bye!
(Friend exits the room)
Squishy Hippo: Oh god I hate her.
Jack: Dude I wanna fuck that chick.
John: Maybe, dude. But she's a Squishy Hippo!