It's wrong to kiss your relative.
Mark is drunk at a party with his friends and his sister.
Mark wants to kiss someone.
Mark leans over and kisses his girlfriend who is sitting on the couch with him.
Mark leans over and tries to kiss his sister who is on the couch with him.
Mark's girlfriend kisses him back and asks him if he wants to dance with her.
Mark's sister slaps him across the face and his friends all start to laugh at him.