Wikipedia
Bugchasing is the practice of pursuing sexual activity with HIV-positive individuals in order to contract HIV. Individuals engaged in this activity are referred to as bugchasers. It is a form of self-harm. Bugchasers seek sexual partners who are HIV-positive for the purpose of having unprotected sex and becoming HIV-positive; giftgivers are HIV-positive individuals who comply with the bugchaser's efforts to become infected with HIV.
Bugchasers indicate various reasons for this activity. Some bugchasers engage in the activity for the excitement and intimacy inherent in pursuing such a dangerous activity, but do not implicitly desire to contract HIV. Some researchers suggest that the behavior may stem from a "resistance to dominant heterosexual norms and mores" due to a defensive response by gay men to repudiate stigmatization and rejection by society.
Some people consider bugchasing "intensely erotic" and the act of being infected through the "fuck of death" as the "ultimate taboo, the most extreme sex act left." People who are HIV negative and in a relationship with someone who is HIV-positive may seek infection as a way to remain in the relationship, particularly when the HIV-positive partner may wish to break up to avoid infecting the HIV negative partner.
Others have suggested that some people who feel lonely desire the nurturing community and social services that support people with HIV/AIDS. It has also been used as a form of suicide.