As hard as nails
If something is as hard as nails, it is very strong. If somebody is as hard as nails, they tend not to feel sympathy or other positive emotions.
Be hard on something
To be hard on something is to cause damage to it.
To do something the hard way
To do something the hard way is to have a bad experience doing something.
Give someone a hard time
To give someone a hard time is to be unpleasant to him or to criticize him a lot.
He always gives his employees a hard time.
Hard at it
To be hard at it is to do something in a fast way.
Hard to take / swallow
When something is hard to take or swallow it is difficult to accept or deal with.
Her mood swings are a bit hard to take at times.
Learn the hard way
To learn something the hard way is to learn how to do something by making a lot of mistakes.
No hard feelings
This is an expression you use for telling someone that you are not angry with them after an argument.
Take a hard line
To take a hard line is to deal with someone or something in a strict way.