A hep swivel is diverting something with a completly irrelevant question or statement to the subject of conversation. To be used to change the subject, especially when you don't like where the conversation is going.
Valarie: Bobby, we need to talk about our relationship....
Bobby: You're friend Janice called. I think she mentioned something about shoe shopping.
Valarie: Loveyoubye! *SLAM*
Bobby: Phew, saved by the old hep swivel.