Is it rude to ask your professor to NOT put you as co-author of a paper? I am working as a research engineer for my professor. He told me to write a conference paper from the master’s thesis of one of his graduate students, since I am working in the same field. After reading the thesis and analyzing the student's results, I found that most of the work is of low quality and does not justify a publication. I told my professor that there are several inconsistencies in the results and several misleading claims, but he told me to continue writing the paper to the best I can given that “I have experience with paper writing and that I can present the work in a light that could get the paper through peer review”. 

Now that I am almost done with the draft, I don’t want to be an author of this paper given the facts. How can I talk to my professor asking him to not put me as an author without sounding rude?
To elaborate on the comment by Roland.

If you wrote the paper and analyzed the results, you have a strong claim of ownership on the paper (along with the graduate student who got the initial results). Depending on the depth of your analysis you may well be the lead author so it’s your call by right. 

If your professor is pushing for the result to be published then your name has to be on it. If you refuse it can’t happen. If they choose to publish without you it’s ethical misconduct and grounds for retracting the paper from wherever it’s submitted to.

The only diplomatic avenue here is that you push to correct the issues and then submit. Otherwise, politely say that you think the paper is not ready and that it is not publishable in its current state.