not have two brain cells, pennies, etc. to rub together
not have two (something) to rub together
To be totally bereft of or lacking in something. Oh please, that fool doesn't have two brain cells to rub together—there's no way he could pull off such an elaborate plan! There were a few months during college when I didn't have two pennies to rub together, surviving off the handouts of my friends and housemates.