No one loves to hear bad news. Especially, if the news is something that makes a huge impact on your overall business and work ethic. In fact, you never know how an individual will react towards something that is "bad" or of a negative nature. Although delivering bad news is very hard because everyone is different and impossible to predict, it is something we must do if that person (in this case, project manager) is not working up to standard.
The important part of delivering bad news is simply "knowing" the person. If you know nothing about the project manager, including his/her work ethic and overall business contributions and benefits to the business, you need to simply find all of that out. Take sometime to separate the individual from his/her job and position, to focus on who this individual is as a person. If you haven't done so, it is also best to prepare yourself with questions you may expect the project manager to ask you. Perhaps, think of the most common and make sure you have an answer for them, because they may put you on the spot.
It's ok to be professional, but do not be afraid to be a little personal. The key is being impersonal, yet personal. This doesn't mean befriend them. This doesn't mean they must be your best friend. You want to find out what you can, because when you present them with bad news, you can use several alternatives in your method, involving things you know about them (good things that is) that will give them hope.
What kind of bad news are you delivering to the project manager?
When presenting bad news to project managers, it is best to be passive, yet alert, but also direct. It is important to use tact, no matter how they act because you are the professional and you are the person that has a standard to set. To react in a negative sense would be not only selfish, but rather foolish. You are also representing a company and therefore, should always respect the company you are representing.
After you deliver the bad news, it is best to tell them what they want to hear, without being personal. For instance, you used tact in your approach, now you need to sympathize, although empathy works best. Perhaps, think of something that occurred in your life and use that as an example of what it has done to improve your work ethic and overall stance. Give the project manager the same guidance and hope, as no hope should ever be lost.