This is usually stated when a college professor is so easy that all you have to do is literally have your "ass in seat" to achieve an A grade for the class. College students generally know which professors are AIS by word of mouth rumors.
Chandler: Hey Joey, take a community college course with Professor Ross, and you are guaranteed an A grade for the class as long as you attend class.
Joey: Are you saying Ross is an AIS professor?
Chandler: I am totally saying he's an AIS professor.