Thanks, everyone, for your suggestions and concern about Office Stalker, that weird older guy who suddenly started constantly talking to me. I mentioned it to a couple of cow-orkers the day of the second incident. It turns out that he's apparently on this medication, possibly Paxil, that has made him extremely chatty to everyone, not just me. Word is that he's taken to jogging around the neighborhood and passing out his phone number to all the neighbors he encounters. A pill that makes you too outgoing - amazing.
Anyway, about 20 minutes after the shoulder touching incident, he approached me again. "I hope you have a good sense of humor," he said. "No, not really," I answered, as frostilly as I could muster. (This took place outside my cubicle, which is plastered with pictures of The Simpsons and SpongeBob, Far Side and Dilbert comics and amusing, fun bric-a-brac.) "Oh," he said, and beat a hasty retreat from my little corner of Marketing.
Since then, he hasn't bothered to enter my cube or engage me in banal conversation when we pass each other in the halls. Which is a Very Good Thing.