How to evaluate student team members who did minimal work on a team assignment? I have this class where at the beginning of the term the lecturer pretty much randomly creates groups of 5 people (who usually do not know each other at all) and assigns them a project. 

At the end of the term we do a presentation and a written exam. A friend of mine who took this class before told me that the lecturer will ask me to evaluate the other members.

Three people in our team were just terrible. They did not care at all, they did not even respond to emails, never arranged any workshops, and only came once or twice to other workshops we suggested, with the only one person remaining in the team besides me; so two of us pretty much did the project. 

However, I really do not want to tell in the paper that they did not do anything. I do not care that they did not do anything, and I do not feel comfortable talking behind their backs. It should be the lecturer's responsibility to figure out who did what by asking the right questions in the exam and in the presentation, I believe.

So do I just leave those parts blank in the exam, or explain how I feel?
Evaluating your fellow students should be a supervised exercise of constructive criticism, e.g., after a presentation given by them. I hope this is what the lecturer will do.

Anyway, if you are assigned this you need to do it. I would give the bare facts for the students that didn't really involve themselves. I.e., I would state exactly what each team member contributed to the project. And if they only suggested a color for a button then I would state that. I would then proceed with providing an honest evaluation of the student that did all the work with you and for the others just say that they could have involved themselves more in the project.

I know that this feels a bit like being a tattletale, but it is actually them that behaved unethically by not working with you on the assignment. The only thing you should have done differently is having a frank discussion regarding their involvement (with them and with the lecturer) at an early stage. Resolving issues like this during team work is actually something you need to learn during your studies. And it appears like you haven't. Thus, you should add this as self-criticism to the evaluation and ask the lecturer to teach you methods of handling such issues.