I second this! Only because Cartman can be an asshole, but yet likeable, thus your asshole is likeable. You thought of funny things to keep you enjoying the anal penetration.
Also you didn't win the lottery lest you would be long gone by now living a high life. As for taxes, who gives a shit? It is a fact of life. You have accepted that and would go out to get fucked in the ass over it.
Thus it has to be Cartman.
At same time it must be something else. Like: OMG! This cock feels so huge up my ass! Loud moan following thought...