swim with sharks

1. Literally, to be in the water with sharks. My brother is a real adventurer—he's bungee jumped before and has even swam with sharks!

2. To be involved with cunning, possibly dangerous, people. I know you think you're a hustler, but you're swimming with sharks now—you could lose all your money against these guys. Before you start swimming with sharks, consider this—the last guy who went into business with them wound up dead!