The term "big six" or "big green" refers to expatriates of Mainland China. These labels were created by Hongkongers who detest the influx of Mainlanders in Hong Kong or other hotspots for Chinese immigration, such as Vancouver and Toronto.
Although these characteristics are neither universal nor exhaustive, they shall help you differentiate between the superior Sino races (Hongkonger and Taiwanese) and the inferior Sino race (big sixes):
1. Big sixes speak almost exclusively in Mandarin that contains a disproportionate amount of tongue-rolling and spitting. In addition, big sixes commonly speak at volumes 20 or more decibels louder than required. At the political level, big sixes are known to speak with dramatic pauses -- these often make the politicians sound stupid rather than self-important.
2. Big sixes have facial features that suggest too much inbreeding or working on the farm. Moreover, their teeth are stained with tar due to constant cigarette smoking.
3. Big sixes completely lack fashion sense. For the poorer population, they will dress in clothes that seem to come from the extra-cheap section in a thrift store. Their clothing often goes unwashed for weeks to months. For the big sixes who are well-off, their attire exudes the stench of wealth. Although this phenomenon has not been investigated by psychologists, the fact that rich big sixes cover every available facet of their bodies with LV monograms or Burberry patterns suggests that they are afraid people don't know they are wealthy.
4. While sophisticated human beings prefer standing or sitting, big sixes would much rather crouch with their legs wide apart near the kerb. These postures can be easily observed at busy bus stops in Vancouver. What goes unknown to the general population is that big sixes, both male and female, take the same position to relieve themselves at public washrooms. Hence there is all the more reason for you to wipe of that toilet seat before you go.
5. Due to the rampant lack of education in Mainland China, big six children are usually the ones to misbehave in public areas and on public transportation. Unbeknownst to both the children and parents, these annoying behaviour outbreaks contributes greatly to the general dislike of big sixes.
6. They smell. Really.
Note to readers: Hongkongers and Taiwanese alike find it a great insult to be racially grouped together with the big sixes. Therefore, Westerners should take care when they show negativity towards Chinks. The populace you are referring to (dissing) is probably the big sixes.
A-kun: "Ergh. I just took the MTR and it was crammed full of big sixes."
B-kun: "That must have smelled."