it's ill jesting with edged tools

proverb Casually engaging with dangerous people or things is likely to cause harm. You're right, I don't speed when I'm driving in the rain, not even a little bit. That's because my mom taught me that it's ill jesting with edged tools. You're picking fights with known gang members, Tom. I know you're a tough guy and all, but it's ill jesting with edged tools.