I am collaborating with a professor (and thus one of his PhD students). The professor likes me and my idea, but the same cannot be said about the PhD student.
The PhD student takes much longer than he normally would to do simple tasks which are essential for the project, and regularly points out flaws in the research design. Every research has its limitations, and I agree those are limitations, but I don't agree that they are nearly as severe as they are made out to be.
If interpreted generously, the PhD student is less enthusiastic about the project. If interpreted harshly, the PhD student is actually trying to sabotage the project.
Obviously I only want to complain to the professor as a last resort. What can I do to make the PhD student more enthusiastic?