Be recklessly irresponsible, unreliable, or deceitful, as in This reporter is known for playing fast and loose with the facts. This term probably originated in a 16th-century game called “fast and loose,” played at country fairs. A belt was doubled and held with the loop at table's edge, and the player had to catch the loop with a stick as the belt was unrolled—an impossible feat. The term was already used figuratively by the late 1500s, especially for trifling with someone's affections.

To behave dishonorably; to make a promise and fail to deliver on it: “It sounds like a good deal, but I hope that real estate agent isn't just playing fast and loose with me.”