1) tough love 严厉的爱

You gotta use a little tough love to discipline your puppy!

Or he won't listen to you when he grows up!

2) tough cookie 非常强的人

My Grandma raised 10 children on her own! She is one tough cookie!

3) hang tough 顽强不屈

I always give in too easily! I gotta hang tough!

4) When the going gets tough, the tough get going! 困难越大，让人越有斗志!

I lost my job yesterday. But I am determined to succeed!

When the going gets tough, the tough get going!

5) tough luck 真倒霉， 运气不好

You missed 3 classes. So you get a failing grade. If you don't like it, tough luck!