Deprived Boston sports fan

My friend has recently started to teach Chinese lessons privately to students. She, like most of us foreigners in Japan, signed up to a teaching match-making service website which provides potential students who want to study any language with connections to teachers who want to make some extra money on the side. Seems like a good thing to do right? After all, we all could use an extra 30 bucks per hour doing easy work. The only problem is, there are some real wackos out there who get confused by the word "teacher" with "potential girlfriend/boyfriend". My friend is a attractive young Chinese lady and she has had the unfortunate experience of teaching a trial lesson to a guy who's objective is "You are the reason why I want to learn Chinese". Translation: the guy's really just looking for a date. Probability of being a stalker at this point...5-10% So my friend asks me for advice on this situation. Since the guy isn't really serious about learning Chinese in the first place, I told her that she should just drop him before it gets any weirder. She did just that, except that the guy has been emailing her, a lot. Probability of being a stalker at this point...25-40% I wasn't sure how often the guy had been emailing her, but it was enough to creep my friend out. Anyways, she emails me last night and tells me that the guy wants to apologize to her in person and is in the immediate area of her work. She's legitimately scared at this point.
Stalker probability...50-75%. I go to my friend's area, since I was close by anyway, and decided to walk her back to the station. We meet up, had a drink in a bar, and her phone was buzzing every 2 minutes. Yep, it was that dude.
Stalker probability...75%+ Needless to say, I was able to catch the last train home, had a nice talk with my gf, confirmed that my friend got home safely, and went to bed at 1:15am. Of course, I had to wake up 6am this morning to get to school and teach, but heck, it's the long weekend now!