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Phrase(s): play with fire
1. Lit. to use fire as a toy; to experiment with flames and fire. • Jimmy! I’ve told you never to play with fire! 2. Fig. to do something dangerous or risky. (Usually playing with fire.) • Be careful with that knife! You are playing with fire! • If you mess with Max, you are playing with fire.
McGrawhill's American Idioms And Phrasal Verbs
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Take part in a dangerous undertaking, as in You're playing with fire if you go behind his back and commit his department. Although the idea behind this metaphor is ancient, it was first recorded only in 1655.
American Heritage Idioms