This probably doesn’t quite meet the definition of a sick joke but it’s close enough for me to get a laugh.
Jake was dying. His wife sat at the bedside.
He looked up and said weakly: “I have something I must confess.”
“There’s no need to, ” his wife replied.
“No,” he insisted, “I want to die in peace. I slept with your sister, your best friend, her best friend, and your mother!”
“I know,” she replied, “now just rest and let the poison work.”