This is the Québecois
equivalent of "Chink
" in English. I'm actually not sure if that's the way it's spelt, it might be "Chingtoque" for all I know. I've always thought it was spelt this way however.
I've no clue where this expression comes from. It's very dissimilar from Chink (or its predecessor) or Chinois, or Chinese. What is very likely is that Ching is simply a recognized sound from the Chinese language and -toch is simply added to be derogative. Ching-Ching is also an older (circa 50's, 60's in North America) derogative word. Lesser than Chink if you ask me though.
I've been called Chingtoch many times. When I was younger, it wasn't as hurting, because I didn't know racism. As I grew up however, I did not know how to react to such words. When I was in High School, I ignored it, I even used it myself, but I've also kicked the living shit out of some people that have known to utter such words. The Living Shit.