How to deal with an innappropriate comment from a japanese co-worker?

Question:

Im going to keep this as brief as possible.

I am a Seishain at a medium sized Japanese company. I am based at one location at the company, but during the week I go to other locations, for meetings, or whatever my company needs.

I was at a different location for my last 2 hours of work this afternoon, which happens to be an elderly care day centre, and I was leaving to go home, and at the same time the customers were leaving to go home, and the staff were helping them.

One female staff member (who I have only had VERY passing contact with until now - only "aisatsu" really) came up to me, rubbed my stomach and told me I looked pregnant. I am not pregnant. Everyone knows I am not pregnant.

I am not "Japanese size" but nor am I obese or overweight. However I do have a child, so granted my stomach isn't as flat as it used to be. But I took this to be offensive, and pretty upsetting. I am not Japanese, but since I have lived in Japan for so long I have kind of got used to not being touched up by virtual strangers, and ... I was a bit flabberghasted.

I was pretty shocked at the time (no tears or anything though), and one of the people who I work with when I visit this centre picked up on it, and he said not to worry, as it was just a joke. But ... I still feel pretty uncomfortable. I think it is wrong to make jokes with people who are practically strangers to you. If It was someone I work with everyday it would be different ... do you think?

How should I deal with this situation? Go to my general line manager and tell her what happened? Find a reason not to go back? Or am I being oversensitive and should I just ignore it? I must admit, it has left me feeling uncomfortable, and reluctant to go back. I can guarantee that she would not have said it to a Japanese person.

Also .. I usually wear a suit to work, but today I Was wearing a slightly floatier dress with a pair of leggings. A little more casual than usual, but nothing inappropriate. And I have lost quite a considerable amount of weight recently. This comment was nothing more than nastiness, and I would appreciate some objective opinions on how to deal with it. Im not going to quit over it, but I just would like some advice. I really love my job, but its my first job with a Japanese (non english speaking) company.

Please be nice ... Im a bit upset.

Answer:

What the female colleague did to you is definitely an unacceptable thing. She obviously lacks basic manners toward her colleague. Even if it happened between close colleagues, it should be very delicate & personal thing to be referred to. At least in Canada, where I currently live, people would take it seriously and even someone beside you say "that's very rude!!"
I'm not sure how old the colleague is, but she seems just immature, ignorant or insensitive. If I were you, I would try to tell her calmly how I felt uncomfortable, or bring it to 'personnel department' (preferably female staff)
But you should not mention 'cultural difference' thing this time.
(edit)
People having common sense would not touch your belly and say "you look pregnant"
While some people don't care much, the fact is that you felt uncomfortable and still now. (that's why you posted this) I won't say it is a 'harassment', but these feelings are to be judged only by the person who felt uncomfortable and worry about future. As a woman and as your co-worker, she should learn from this mistake.