Drunk Men... and Knitting

I am amused sometimes by the random conversations I end up having with people in Japan. People who speak to me for no other reason than I am a foreigner. A perfect example is the conversation I had with a semi-tipsy salary man on a late train a few months back. The original conversation was in Japanese, an English recap is as follows:

STS - "Wow... You are knitting!"
me - "Yes, I am."
STS - "A scarf?"
me - "Yes, a scarf."
STS - "Wow, your Japanese is good!"
me - (all I've said is a few words buddy, don't get overexcited!) "No, not at all."
STS - "It is getting warm, you had better hurry up and knit it soon!"
me - "Yes, I should!"
STS - "Your Japanese is good!"
me - "No, not at all. You see, I'm a student."
STS - ...

STS - "So where are you from?"
me - (I knew this one was coming!) "Canada."
STS - "Your Japanese is really incredible!"
me - (this again?!) "No, not at all."
STS - ...

This conversation went on, as every few minutes STS asked me another random question (about Canadian winters, did I know how to ski, how much could I knit in one day, how did I switch colours for the stripes, etc). I would reply. He would make impressed noises and compliment my Japanese. I would do the polite Japanese thing and refute my abilities and he would lapse into impressed silence. A few minutes later he would rouse himself out of his drunken stupor and come up with another question and we'd start it all over again. The entire conversation (if you can really call it that) was amusing and I felt in no way threatened by the guy, so I had no problems chatting with him (although I made sure to give him no personal info).

Being chatted up by drunken Japanese men of any age is a somewhat common occurrence for me (and many foreign females in Japan, I am sure). Most of the time said conversation can be avoided by simply ignoring the guy and moving away. While there are likely others who would disagree with me, I have found that this tactic works well for most circumstances. It is unlikely that the guy will pursue you or cause a problem. This is not always the case, I realize, and can be a bit of an issue if you are, for example, riding a long-distance train and are unable to get off or otherwise extricate yourself from the situation. Having headphones on (even if no music is actually being played) can help with the whole ignoring thing, and if spoken to then feigning no comprehension of Japanese or English can also work (a stream of random French caused one particular guy to move off rather quickly!).

As a result I have developed a defense mechanism. When approached I tend to brush strangers off as quickly as possible. After one incident, the comments of my male foreign friend got me thinking, and after another incident, this time with female Japanese friends, I got to thinking again. I know it is a defense mechanism, and in both of these instances it helped. It got me (and my friends) out of a potentially uncomfortable situation before anything happened. The trouble is what about when the person I'm brushing off is not drunkenly trying to hit on me in non-existent English? What about when it is a friendly and somewhat lost foreigner trying to chat me up on the train? Or when it is a kindly and cute Japanese guy with excellent English offering to help a lost-looking Canadian in the supermarket dairy aisle? How and where do I find the line between ignoring the drunks and crazies on the one hand, and not being rude to people who are honestly trying to help or be kind?