How to address bad research experience I want to apply to CS PhD programs this year. Just a litte background: I did my BS and (non thesis) MS in EE/ECE at the same school. During my BS I did two semesters of undergrad research that went fine and gave me valuable experience. 

During the second (last) semester of my MS I took on for-credit research with a professor. We got all the forms settled and decided on a project. However, after a certain point (me reading papers to catch up on the work) he stopped responding completely. I sent him emails frequently asking for resources to start my project (required some simulation resources at the least), but he never responded. I also tried to catch him at his office whenever I was free during the semester but completely failed. At the end of the semester I was awarded a B. Should I even address this on my application? Would it look bad to not include this experience at all?

The other weird caveat is that this is the only B throughout both of my degrees, so it is pretty noticeable.
If I had no further information about what happened and it was me, I'd not mention it on application materials. That is, not try to explain it away. List it as a research experience on a CV, without other explanation. I'm assuming the grade you got is on a transcript. So, it isn't something you are hiding, but just not emphasizing. 

If you are asked about it, you can honestly say that you don't understand the grade and that your supervisor stopped replying to your updates. You don't know why that was. Things happen. They aren't your fault. If the experience itself was valuable in setting your thinking then it was a net plus in spite of the mediocre grade. You can say those kinds of things. 

But, as I mentioned in a comment, it would be good to also know why it occurred. I think I'd refrain from explaining it in written materials in any case, but you would have some additional background if the issue comes up.