When you give someone “the slip” it means that you sneak¹ away without being noticed. Usually, it is a mean or rude thing to do if you give your friends “the slip” as in this scene. However, if you give an enemy or someone you are trying to avoid “the slip” this is a good thing for you, since you probably didn’t want to be noticed.

　　slip的本意是滑倒、滑动，但在俚语中可用于特指某人在不为人知的情况下偷偷溜走。

　　例句：

　　1.Can you believe it? She gave me the slip! I thought she liked me!

　　你能相信吗？她溜了！我以为她喜欢我呢！

　　2.If you give me the slip again, I’m going to be really mad.

　　你要是再溜，我会非常生气。