Final answer:
The student's assumption about their new roommate being a slob demonstrates the Fundamental Attribution Error, as they are attributing the messy behavior to her character instead of her stressful circumstances.
Step-by-step explanation:
When the student assumes that their new roommate is a slob because she leaves dirty laundry all over her room, without considering her current circumstances such as taking finals and working long hours, the student is demonstrating the Fundamental Attribution Error. This error occurs when we overemphasize dispositional, or personality-based, explanations for behaviors observed in others while underemphasizing situational explanations. In other words, the student is attributing the roommate's messy behavior to her character, rather than the stressful circumstances she is under.