to be a headache

• 最伤脑筋的问题

  extremely troublesome problem

• 犯不着为这事伤脑筋。

  It is not worth troubling oneself over this matter.

• 这事真叫我伤脑筋。

  This matter has caused me a great deal of bother.

• 同这种人一起工作实在伤脑筋。

  Working with this sort of person is a total pain.

• 我们伤了不少脑筋才猜到了。

  We eventually guessed it after a lot of trouble.