1
general::
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.
American Heritage Idioms
2
general::
Phrase(s): play fast and loose (with someone or something)
Fig. to act carelessly, thoughtlessly, and irresponsibly. • I’m tired of your playing fast and loose with me. Leave me alone. • Bob got fired for playing fast and loose with the company’s money.
McGrawhill's American Idioms And Phrasal Verbs