I honestly don't know what to say since what you told is almost unbelievable. I guess you're just really really and I mean really, unlucky. i myself dislike many things in Vietnam, but one thing I found amusing is how most tourists and expats found this place to be...amazing. I love Vietnam, it's home, still, I'm still amazed with that. And what stunned me more from your post is, you experienced these bad things in HCMC, where, arguably, friendlier compared to the North. But to be honest, I think it mostly came from your perspective, I mean the way you see things. It's like you're having a "culture shock". for example:

"They would allow you to cross the street without nearly running you over, wouldn't honk the horn" -> while this indeed seems rude, but at the same time, it's just the way it is here. that's why when I first was in singapore, I was very surprised when a bus stopped when it saw me crossing a street, and the driver signalized for me to just cross and ignore him. but that doesn't necessarily mean we are rude. God knows how many times I dodged someone who crossed a street :D that's why people said the 1st ultimate tip to cross streets here is, just do it. Just cross, the vehicle will dodge you.

for the hospitality at restaurants and such, I guess you've been to really almighty places who think they're too good at their business to care about customer services. there are a lot of them here. but that is just the minority. Most of the time, I have no complaint about it, sometimes I even get...uncomfortable when they overdid it. again, you are, I guess, too unlucky.

everything, everywhere, has its pros and cons, has its bright and dark side. I was ripped of from DonMuang to central BKK as well. but that's just a very tiny bad experience compared to other friendly warm and welcome events I had when I was in BKK, and Phuket, or even Pattaya - where not so many people fun of. I went to Bali and thought OMG why this place they are so nice. I went to Singapore, and despite the very calm and pressure life they have as a well-developed country, I had the most interesting encounters with strangers I met at random places, even though some of them I found very reserved. I mean, it all depends on how you see things, and, how you overcome the initial culture shock. I witnessed an English guy then came here, tried to experience "the other side of the world" but he got the culture shock and climate shock so bad, that he could not recover from it and thought VN isn't a nice place, at least for him.

i hope your later experience will get better :)