For me, it has always been an accumulation of tiny shit that builds up and eventually some tiny thing will tip the balance and I turn into the ranting laowai.  I don't think I could ever point to just one thing.

However, most things that set me off have one base commonality. A lack of common courtesy.  The simple fact that courtesy to others is not even a thought that happens.

I am not saying that everyone in China is like that.  But it happens often enough where I keep the local tavern in business. 

Mostly the same as Xpat John the biuld up of small things over a few days
When I first went to China I found the stareing got to me after a while
until I lernt how to deal with it .
most of the things that get to me in China are totaly oppitsite to back home and are not important
However I have gone off my nut at a bottle collector one day in a mall
or the odd statement on this web site.

Actually, that isn't true.  Now that I think about it, there was one day, one event that happened and if the outcome were different, I would have gone on a murderous rampage.

My twin boys were about 6-8 months old when I heard about the tainted milk powder scandal.  Thankfully my Chinese wife was smart enough not to even entertain the idea of using Chinese milk powder, but if she had used that brand, I would have died trying to kill every exec and supplier of that company.

That day, the "anything for money" atmosphere really hit me hard.  On that day, after finding out my boys weren't affected, I was ready to pack it all up and leave this country for good.

But my wife, at times, has a much cooler head than I do sometimes.  She was able to convince me to stay.

My first 2 days here, I was alone in the middle of nowhere in the house of a chinese friend of my chinese teacher that had offered himself to help me finding accomodation and my way around the first few days. Instead, he picked me up, took me to his place left for work and came back the day after with food, to go back to work again... I ate like twice in 3 days! I had a couple of online 'friends' that turn out to be amazing and got me out of there.

Apart for those two days...the first time I went to the Great Wall I fell down and twisted my ankle...so I can say I had a pretty horrible first month.

However the next year and a half have been great!

yesterday i had them finish my root canal . the first 3 trips to the dentists were ok. and after the first hour i thought they were done and i would come back later to have them place the crown or cap (whatever the term) . after the next 3 hours of drilling and almost choking to death (taking the impression) they put what i thought was a temp crown / cap and now i cant chew becoz it's too big . it hurts like hell i want to rip the damn thing out but it seems they use super glue here. monday i will go back and ask them to file the damn thing down to 3/4 the size. 
i need to learn to speak chinese and i should've just had them pull the tooth out

Ate something crazy and ended up having the green apple splats in a storm drain in a dark alley because the neighborhood gate that led to the public bathroom was locked and mine was broken. Thought I was going to die.