I actually had to Google "eyebrow flash" since I wasn't 100% sure what you meant. Anyway, I've never heard of that being offensive and I've lived and worked here just over 2 years now. Granted, a slight bow is standard here so maybe it just never gets used.
umm.. how can I explain it.. when you re talking to someone and do eyebrow movement such as, left brow goes down and right brow goes up. something like that
Ah, I got it - it's where you raise both at the same time very briefly to acknowledge you seeing someone else. Your teacher said it's offensive? I'll have to watch out for that :P
Hehe, this kind of thing always gets me searching the web. ^^;; At least this time, there wasn't something else I should be doing.
For those curious, here's video of eyebrow flashing: http://cas.bellarmine.edu/tietjen/RootWeb/flash.mpeg It's a universal sign of recognition, often used as a non-verbal greeting or to acknowledge what someone has just said or done, usually accompanied by a smile or nod.
And from what I've found so far, it looks like the eyebrow flash is very limited in Japan - the scholarly sources said it's restricted mostly to children, and one said it is "considered suggestive or indecent". One book said that they restrict it to children and familiar adults. Most articles related to the workplace (and two about flirting) outright said it is rude and can have strong sexual connotations. So I would imagine that it's largely like anything else that shows great familiarity - you're not going to use it with people in general, but with kids and good friends it's okay.
"The Japanese, who are reserved in social expressions among adults, use it mainly when greeting young children..." from a psychology textbook.
...Now I'm going to be watching my dramas and looking for eyebrow flashes. The back of my mind has been trying to remember for the last five minutes if I ever saw any of the guys in Gokusen do it. :\
