We were in Japan over Christmas, where there are no service charges, and when we tried to leave a few Yen at a little Hawaiian place in Nagano - genuinely about HK$3 - it really confused the staff. They pretty much chased us with the change, then when we waved it away, they 'forced' us to take a couple of little candy canes from their Christmas display to make up for it. Needless to say, this being Japan, the service had been excellent and friendly, and elsewhere would have fully justified a tip.
It can go too far the other way as well...