Like a wank bank for dudes, the Mast Cast is girl's list of hot dudes she thinks about when pleasuring herself.
Girl 1: Ugh, another Valentines Day alone!
Girl 2: Sounds like a great night in with your mast cast. Who's your number 1?
Girl 1: Oh, Ryan Gosling, obvs! I just play that scene from the Notebook over and over again and I get off in no time.