A: Why didn't you invite her to your birthday party?
B: Because she didn't invite me to hers. It is just tit for tat.
A: Why do you take it so seriously?
tit for tat
Tit for tat的意思是“以牙还牙”。
E.g. He hit me so I hit him back. It was tit for tat.
E.g. I told her if she did me any harm I would return tit for tat.
E.g. Tom pushed Polly off her chair. Then she got up and gave him tit for tat by pushing him off his.
E.g. They had a warm debate and the two gave each other tit for tat.
take it seriously：放在心上
E.g. What he said was just rant. Don't take it seriously.
E.g. He was joking. Don't take it seriously.
E.g. When people ask you to do something, you should take it seriously.
E.g. I take this seriously. It's a matter of principle.