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。