The two countries have each expelled another diplomat following a round of tit-for-tat expulsions.

在一轮以牙还牙的驱逐行动之后，这两个国家又分别驱逐了一位外交官。

《柯林斯英汉双解大词典》

When you are eating at a restaurant, the server may tell you bon apptit, which means good appetite, or enjoy your meal.

VOA: special.2010.04.18

The speculation on the street is that it was a tit-for-tat assassination between rival gangs.

NPR: Film Adds Fuel to Venezuela's Social Fires

"For the first time, we are getting into a tit-for-tat syndrome, " he said.

CNN: Israel attacks Syrian positions in Lebanon

Adarsh Sinha of Barclays Capital thinks the Swiss move will not be the start of a tit-for-tat round of devaluations.

ECONOMIST: The terrible temptation to depreciate