wouldn't if I were you

(I) wouldn't if I were you.

Fig. a polite way to advise someone not to do something. Mary: Do you think I should trade this car in on a new one? Sally: I wouldn't if I were you. Bob: I'm going to plant nothing but corn this year. Sue: I wouldn't if I were you. Bob: Why? Sue: It's better to diversify.
See also: if