"Chocolate Peanut Bush" is a slang term for Hemorrhoids, which are also known as "Piles" and sometimes more commonly as "Bum Grapes".
It's generally used by those blessed with nice, normal arseholes to mock those that have guts that are literally trying to escape out of the back door.
Jim: "Blimey! I just had a check around my arsehole and my Chocolate Peanut Bush is in full bloom... Have you got one of those donut shaped cushions I can sit on?"
Bill: "You're not sitting on any of my chairs you filthy, Chocolate Peanut Bush growing bastard... special cushion or not!"