"Many people will also greet all Asians with konnichi wa and fold their hands like for the Thai-greeting. This may be annoying, but I'm sure they just try to be funny, instead of hostile."
This is so true.
I've met people greeted me "Konnichi Wa"(Japanese) and "Ni Hao"(Chinese / Mandarin), with their palms pressed together(Thai greeting), and then told me the location of the best Pho(Vietnamese cuisine) in town. I didn't know I can be Japanese, Chinese, Thai, and Vietnamese at the same time before. LOL. But as long as they were nice and friendly, then I didn't mind those generalizations.
Regarding the slanted-eyes gestures, I had only one encounter. Probably because I do not have particularly slanted eyes, nor do most ethnic Chinese, I would say.
One woman greeted me first, but when she asked me whether I was Chinese, she used one hand to pull an eye back as if it was a necessary explanation of what she was talking about.
What's ridiculous of those gestures is that many ethnic Chinese like myself don't even have that particularly slanted eyes.
Just take a look at the passengers on the street of Taiwan, I would say maybe only 3 out of 10 people in Taiwan would have that particular slanted eyes(and I didn't even notice those people's eyes that much until I found it was in fact a joke in Western cultures), the other 7 have eyes that are of medium size and shape.
I think the mockers who are still doing those gestures nowadays are just doing it because of the old stereotype, not because of the real size and shape of the eyes of anyone whom they're mocking.
So, all in all, it seems to me that the "small slanted eyes" joke is more like the old lame joke of some non-Americans mocking "Fat Americans", while those mockers themselves may be in worst body shapes than most Americans.
One example of MLB player Bruce Chen.
He actually look a bit Latino, and he doesn't have the stereotypical small slanted eyes.
However, his Latino teammate still thought it was funny to do those gestures toward him.