skating on thin ice
Engaged in some activity or behavior that is very risky, dangerous, or likely to cause a lot of trouble. I hope you realize that you'll be skating on thin ice if you decide to gamble your employees' retirement funds on such a dodgy investment. Honestly, I wouldn't even mention the new woman in work, or you could find yourself skating on thin ice with your wife.
skate on thin ice
Fig. to be in a risky situation. (Fig. on the image of someone taking the risk of ice skating on thin ice.) I try to stay well informed so I don't end up skating on thin ice when the teacher asks me a question. You are skating on thin ice when you ask me that!