or you can say , you abuse your mind or yourself ..

or you can friendly say , use your mind to benefit or invest , or you can change the word your mind to be yourself ..

you can friendly say listen good my friend , you have to think right with your mind in order to not fall in problems .

If YOU want to say someone that YOUR mind is not right ?? Who's mind is not right? Yours or their's? Are you nuts? You are nuttier than a fruitcake. You have bats in the belfry. Lost your marbles? A few cards short of a deck? Lights on, but no one home? Engage brain before putting mouth into gear. Did you make that up all on your own?

Such a great thread, Luti. In addition to the phrases mentioned earlier, you could ask: "are you kidding me?" or "have you lost the plot?" or "have you lost your marbles?" since you seem to be asking for colloquialisms. However, since it's a conversation between friends, one could just get away with "whatever!"