How to deal with incompatible labmate? I'm having trouble with one of my labmates that is severely impacting my work. He is a more senior student than me, but only has been in my lab for two months since my advisor came from a different university last year, and this student didn't come initially (he was supposed to graduate at the old institution but didn't). 

No one else in the lab works on similar research to me, so when this student came I thought it was nice to have someone around who was experienced in similar research topics to talk to and potentially collaborate with. Right away he told me he planned to publish many papers with me while he's here, and then wrote me up a research plan. My advisor is quite hands off, and he has not mentioned to me that I am supposed to work closely with this student. I like my advisor's hands off approach, and certainly didn't ask another PhD student to write up plans for me. Even though I am a junior PhD student I am very self-directed and thus far my advisor has mostly let me dictate the research problems I work on.

Very quickly, my relationship with this other student has deteriorated to the point where I can't even go to the lab if I want to get any work done (and since I'm in engineering, most of my work is tied to my lab). He talks nonstop. And I do mean nonstop. If I'm trying to work (not paying attention to him), he interrupts me constantly to talk at me, and it is rarely work or research-related. I usually come in early in the morning, and he comes in in the afternoon. As soon as he comes in he starts telling me stories, about his work, about his childhood, his parents, anything. It doesn't stop. When I try to leave after being in lab for 12 hours (say, 8am-8pm) he stops me and criticizes me for leaving "early" (even when I point out if he works from 5pm to 3am it's actually less time in the lab than I've spent), saying I'm not a real PhD student if I don't work all night.

He has decided he will be a coauthor on all of my papers (without my invitation, and without my advisor's input), but he has not done anything. Initially I tried to meet to work out a plan for some experiments, and he didn't show up to some of them and at the others just ended up talking at me. He also touches me on the arm constantly and will stand behind me when I'm at my computer and rub my shoulders. He flatters me constantly, calls me "cute", says I'm going to be "famous" for my work. I don't see him behave this way with anyone else in the lab.

This is a lot of complaining, but the main reason I'm worried is 1) I haven't gotten anything done in the 2 months since he showed up; and 2) I know my advisor highly values students who can work well together (the older students said he fired a couple of students at the old university for refusing to work with one of the other students). 

What do I do? I want to talk to my advisor but don't want to come across like I'm difficult to work with. I'm in a tough situation because this other student is more senior and has a long history with my advisor. I have immense respect and gratitude towards my advisor, but I have only been in the lab for a year (after leaving a toxic lab with a terrible advisor) and haven't yet established a good track record of research results. I've been working at home and hiding out in other labs to try to get my work done, but I can't stay away from the lab forever since I have to build stuff and run experiments. I'm worried my advisor is going to fire me for lack of results (another thing this student tells me constantly). 

Sorry for the long rant, but what should I do? Should I try to talk to my advisor? Should I disappear until I have good results to show so he can't fire me?
You need to have a discussion with your advisor about the situation, if it is as untenable as you claim.

Before you do, however, may I suggest that you consider rescheduling your day, if possible? You said your labmate does not show up until 5 pm in the afternoon, while you arrive at 8 am. That gives you from 8 am until 5 pm to work on your project without your labmate hanging around. I would plan my day to spend as much of the time between 8 am and 5 pm in the lab, and then conveniently "disappearing" to the library between 5 pm and whenever you want to leave. Use this time to catch up on journal reading, emails, and any other tasks that you otherwise wouldn't have to work on because you're busy in the lab. This may give you the time to be productive and get some results to show your value, if you think that's a concern you need to deal with before speaking to your advisor.

The other issue is dealing with your labmate deciding to be a co-author. That's actually the bigger issue here: unless your labmate makes substantial contributions to your paper, he shouldn't be a co-author. Moreover, he shouldn't be deciding unilaterally that he will be a co-author. It's your research, and you should have some say in who collaborates with you. Now it's possible that your advisor might want to get your colleague "out the door" and might ask you to collaborate on a paper or two. However, if that's the case, that should be something to determine via discussions with everybody involved. [Note that the question is "nominally" about undergraduates, but the advice there applies to any research situation.