You can say that again.
Meaning:
Strongly agree with someone.
If you say "You can say that again," you express your strong agreement with what someone has just said.
This expression is used especially when you are complaining about something.
Example:
A: Don't to talk to Mr. Hughes. He's been really grouchy these days.
B: You can say that again. He argues with anyone who talks to him.
Daughter: Mom, this shirt is too small. I got this more than a year ago.
Mother: You can say that again. I will buy a new one for you.