hard as nails

[hard as nails] {adj. phr.}, {informal} 1. Not flabby or soft;physically very fit; tough and strong.

After a summer of work inthe country, Jack was as hard as nails, without a pound of extraweight.

2. Not gentle or mild; rough; stern.

Johnny works for aboss who is as hard as nails and scolds Johnny roughly whenever hedoes something wrong.