An expensive sports car or similarly overpriced automobile that is driven by an asshole in an attempt to impress others.
"I don't know why Mr. Peabody feels the need to drive that horrible new rectumobile. He must be going through a mid-life crisis."
"Gertrude is driving one of those annoying rectumobiles now. Doesn't she realize that everyone thinks she's nothing more than a pathetic old maid with money?"
"There are so many rectumobiles on the road. It just goes to show how many assholes there are in the world."