a thorn in sb.'s flesh/side

1. 某人的眼中钉

He was a thorn in the police's flesh.

他是警方的眼中钉。

be/sit on thorns

1. 如坐针毡; 焦虑不安

He was then sitting on thorns and waiting for you.

他当时如坐针毡, 焦急地等待着你。