be a fox

1. To be sly and crafty. He lets people think he's a buffoon, but he's really a fox when it comes to business negotiations. The novel centers around the cat-and-mouse chase between a police detective and a thief who's a real fox. She may come off as nothing but smiles and sunshine, but trust me—she's a fox!

2. slang To be very sexually attractive. My new math professor is a total fox. All the girls in our class have a huge crush on him. A: "Man, that girl at the bar is a fox. Think she'll talk to me?" B: "Not a chance." Even after being married for five years, I still think my husband's a total fox.