if you know what's good for you

if (one) knows what's good for (one)

If one wants to avoid trouble (one will do or avoid a certain thing). Oh, you'll be on time for the meeting, if you know what's good for you. If he knows what's good for him, he'll stop calling me that.See also: good, if, know

if you know what's good for you

Fig. if you know what will be to your benefit; if you know what will keep you out of trouble. Mary: I see that Jane has put a big dent in her car. Sue: You'll keep quiet about that if you know what's good for you. Sally: My teacher told me I had better improve my spelling. Bill: If you know what's good for you, you'd better do it too.See also: good, if, know