Answer:
Avoidant personality disorder.
Step-by-step explanation:
An avoidant personality disorder is a disorder of a person characterized by a feeling of discomfort socially and avoiding personal contact. In other words, the behavior of a person in avoiding any contact with people, be it socially or in private, and the sensitivity to rejection comprises this disorder in a person.
Stu's avoidance of getting involved in any relationship, be it friendship or even a romantic relationship is an example of this disorder. Stu also has the fear of being rejected, which makes it difficult for him to get ahead in work or give a chance to get involved in any relationship. His fears of being rejected make it hard for him to interact with anyone. And his negativity, believing that he is unworthy or inferior to others helped in this disorder.
Thus, the correct answer is an avoidant personality disorder.