In the example above a thin girl orders a very big meal and the other girl orders a small meal. When the waiter returns with their orders he cannot remember who ordered the big meal. He relies on a stereotype - that individuals who are less thin eat more - to make his decision, and erroneously places the bigger meal in front of the less thin girl.
An example of the representitaveness heuristic.
Representativeness Heuristic
Kahneman, D., & Frederick, S. (2002). Representativeness revisited: Attribute substitution in intuitive judgment. Heuristics and biases: The psychology of intuitive judgment, 49-81.
The representativeness heuristic is a cognitive shortcut that allows humans to make attributions about an individual based on their similarity to members of a particular group (Kahneman & Frederick, 2002). These judgments can be inaccurate because we can rely on stereotypes about specific groups of individuals.
Social Beliefs and Judgments