Answer: A Bunburyist is a person who claims to have to visit or take care of a friend, who is only fictional, in order to avoid his or her obligations and responsibilities.
Explanation: Just to elaborate a little bit on the answer, it can be added that it was Oscar Wilde the one that coined that term. The character of Algernon has a fictional friend, "an invaluable permanent invalid" named Bunbury, whom he uses as an excuse to avoid some of his social obligations, claiming that he summons him to his bed and asks for his assistance. Since Jack also resorts to his allegedly younger brother in order to escape from his social obligations, Algernon also refers to him as a "confirmed Bunburyist." Unlike Algernon, however, Jack does not recognize his morally wrong act, and is determined to "kill" his brother if his beloved Gwendolen accepts him.
