Bo-na-nus, (n.) - The boner that pokes through the anus. (See picture of Tyrannosaurus Rex skeleton for example)
My bonanus was poking through my cheeks at the gym last night.
(Noun): the bonus anal sex you give your man after he's been extra good to you. Combination of bonus and anus as well as boner and anus.
Guy- "I was so good to her this week she gave me some surprise bonanus"
Girl- "if he wants anal from me he's gonna have to earn it. Get some bonanus"