I only want a snack. I'm not very hungry./我只想要一份快餐。我不太饿。

A: Sorry to be late, everyone.

A:  对不起大家，我来晚了。

B: Hi, don't worry - take a seat. What can I get you?

B: 你好，不必在意——坐下。你想要什么？

A: I only want a snack. I'm not very hungry.

A: 我只想要一份快餐。我不太饿。

B: That's not like you!

B: 这可不像你！

A: No, but I had dinner with the family. It's my sister's birthday today.

A: 是的，但是我已经和家人吃过饭了。今天是我姐姐的生日。

B: Well, help yourself. There's plenty of food left.

B: 哦，那你随便。还剩下足够多的食物。

Notes 注释

1. If you go to dinner with friends, and you have reason for not wanting to eat very much, you can explain: I only want a snack. / I only want a snack. / I'm not very hungry. / I'm not very hungry. / I had dinner with the family. / I had dinner with the family. 
如果你去和朋友吃饭，而且你有理由不想吃得太多，你可以这样解释：I only want a snack. /我只想要一份快餐。/ I'm not very hungry. /我不太饿。/ I had dinner with the family. /我已经和家人吃过饭了。

2. If you are surprised at a friend's behaviour, you can say: That's not like you! / That's not like you!
如果你对朋友的举止很吃惊，你可以说：That's not like you! /这可不像你！