I haven't really done too many bad things, just kind of crazy things. Most of them were from before we got the science babies, and some other things.
Before the science babies were released, I had downloaded an Anna and Elsa from the Gallery, as well as a Kristoff from the Gallery. I combined the families. In CAS mode, I had linked Kristoff to Anna through marriage, and made a teen daughter for them. Then I had Kristoff father a daughter with Elsa. Then moved them into a house. The game kept track of their daughters being half sisters, and they got along, but the family tree didn't know how to label Kristoff. He was the father of both girls, but also an uncle to his second daughter. I wanted Elsa to have a child, but didn't want to deal with any dating or romance with her.
Another thing I did was make an Inuyasha family. I just had the parents, and their sons. I had their dad married to Sesshomaru's mother and engaged to Inuyasha's mother. Then moved them all into the same house using motherlode. The game kept track of the family, and Sesshomaru and Inuyasha were half brothers like in their canon source. They got along, but their poor dad got the short end of the stick trying to get with his fiance, while still married. Sesshomaru's mom refused to leave them alone, so their dad had to secretly marry Inuyasha's mom. Then Inuyasha's parents had a daughter in the game, the brothers adore her, but Sesshomaru's mom was angry. Their parents are all still married, but their father spends so much of his time trying to keep the peace between his wives, which effects his relationships with his kids.