The flakiness of many folks here does grate on my nerves sometimes. I think much of it is tied into that horseshit idea of 'face'. Many folks make or express desire to make plans but it often has zero meaning. Of course it happens in our home countries too but perhaps we are better at recognizing it when it happens there. It's easier for us to pick up on body language and tone of voice and other cues back home, here...not so much. When a girl or guy here tells me I am handsome....it does not have the same meaning as when a westerner does. It apparently is not an invitation for sex or a gay dude flirting. 
When invited to dinner or anything else...it's best to assume there is no actual plan unless they contact you again about it. If you call them and ask...it's bad form. Guys and girls alike do this. Yes, it's sometimes frustrating but expectations must be adjusted.
People make empty invitations and empty compliments all the time. I can't tell you how many times I've thought I had dinner plans only to find out later that the person is out of town/visiting family/working/out with colleagues/not feeling well/blahblahblah. Maybe it's me though.
Absolutely isn't just you. This is a cultural thing and it has nothing to do with being male or female, the women do it as well. My (again, Chinese) husband bitches about this all the time. I don't know how many times he's re-told this story to illustrate a point he is making about Chinese society, but I'll re-tell it here again because it is an excellent example of the above.
My husband comes from a town (used to be a village, they got upgraded, woot) outside of Kunming. When we go down to visit his family we have to take a bus to the county seat and then another bus to the village. A couple of years ago we were on our way back to Kunming from the village and were on a small bus just arriving in the county seat when my husband discovers that his high school math teacher was on the same bus! Imagine the coincidence! So they do the Chinese thing and shoot the shit for a bit, and the math teacher tries to convince us to get off the bus, right then and there, and go to his house.
Now this is where you have to understand the culture because a foreigner might have gone along with it that but in reality, this guy had no intention of actually having us get off the bus in this county town on our way back to Kunming, with all of our stuff, 2 kids, etc. and go to his house for dinner. And my husband knew that. So he did the polite refusal thing. "Oh no no no, we're busy." And the guy insisted "oh come on, come have dinner." Back and forth until he finally gave up.
If you didn't understand Chinese culture and the fact that this whole interaction was basically scripted, you might be thinking, gosh the guy really wants us to have dinner with him, maybe we better go. But the truth of the matter is, if we had gotten off the bus and gone to his house, guy would have had no idea what to do. We would have broken the script entirely.
So when we finally did get off the bus (to get on our next bus, back to Kunming) my husband was visibly irritated. I asked him what was wrong. He said, "I hate how fake people are here. Teacher knew we wouldn't come to dinner, so why did he even have to put on the pretense of inviting us?" And to this day, if you want to get him, my husband, on a rant about Chinese society, just bring up this topic and he'll go off.
But these are very very well ingrained cultural norms. It isn't that Chinese men are lying assholes, it is that the culture allows for a certain degree of mutually agreed upon pretense, and that can make it hard for outsiders, particularly outsiders from a country like the USA, where people tend to be straight shooters (about certain things), to navigate.
GZ your original mistake with Jerry, and I agree Jerry was being petty (but again, teenager), was somehow giving the impression to the rest of the class that you were playing favorities. The fact that the chosen kids were female students probably pushed some buttons (and that's not your fault, but this culture is touchy about foreign man/Chinese female interactions, particularly when the women in question are young students). It sounds like there was, again, a load of miscommunication all around. I don't socialize with my students precisely because I want to avoid situations like that but I understand this was a school sanctioned party and it's not like you were having them over to your house.
I think the second guy was following the script. You were supposed to say "sorry, no I can't change it to Sunday, there's no way." The guy was then supposed to make some sort of suggestion about possibly doing something else, you were supposed to refuse, end result is eventually that nothing changes. No where along the line were you actually supposed to change your plans, but the guy had to look like he was making an effort. I honestly cannot see what he would stand to gain from sabotaging your hiking trip and I think you took the whole thing a bit too personally. He was trying to blow you off, the Chinese way.