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!
on thin ice, to be/skate
A hazardous course of action or conversation. “In skating over thin ice our safety is in our speed,” wrote Ralph Waldo Emerson in his essay Prudence (1841). Literally, it is possible to skate over very thin ice without breaking through if one glides quickly enough, but Emerson was already using the expression figuratively.