You shouldn't fake having a dead sibling.
Peter is at a party and sees Lisa, who he finds attractive, and goes up to talk to her.
Peter wants to get Lisa's interest.
Peter ask Lisa about her hobbies and shows interest in the things she does.
Peter decides to try the pity route, and claims he has a sister who recently died.
Lisa finds Peter interesting and agrees to go on a date with him.
Lisa finds out Peter lied about the sister and calls him a creep and tells him never to talk to her again.