An unofficial rule that if your man is in jail or prison, you are allowed to have sex with other men. The man is usually not informed about this. The man the woman cheats with is called a sport coat, or sometimes Jody
guy:Hey girl, we can't do this! You're my cousins girl
Girl: prison clause!
Guy: well, okay then!
Invoked by Otto's wife on SOA so she could have sex with Bobby- Elvis