Place a man in a morgue, he'll try to leave.
Place a doctor in a morgue, he'll go to work.
Place a necrophiliac in a morgue, he'll stay happy for a week.
Morgue Occupants
Explanation
The joke plays on the stereotype of a necrophiliac, someone who is sexually attracted to corpses. Unlike a normal person or a doctor who would want to leave or start work, a necrophiliac would be very happy in a morgue, implying they would find pleasure there. It's a dark and disturbing joke because it uses a taboo topic for humor.