stubborn and difficult to deal with
obstinate - stubborn
Essentially, ‘obstinate’ is a more formal way of saying ‘stubborn’, although while that word can have positive or negative connotations, ‘obstinate’ is entirely negative. This is because rather than the admirable trait of not being submissive or taking a principled stand over something, 'obstinate' implies an unreasonable determination not to change your mind even when it might be best to do so.
My manager is a very obstinate person. She only wants to do things her way and ignores my suggestions.
It was your obstinate refusal to compromise that led to the deal falling through!
His continued obstinacy over staff demands isn’t helping matters. It could lead to strike action.