I hate the laowai thing. Usually I let it go with just a dirty look, but sometimes I'll say something. My husband will almost always say something because he gets offended on behalf of me and the kids. Last week we were at the park and walking around, and this girl, maybe 10 years old, shouts out "waiguoren!" We ignored it the first time, but then she shouted it again and I said "never seen one before?" and my husband said "didn't your parents raise you to have any manners?" He is absolutely done making excuses for his countrymen and women.
Like old said, we heard "laowai," or even "waiguoren," very infrequently in Beijing. In fact, in Beijing, when we heard it from kids, their parents would almost always correct them and say something like "don't be rude," even when they'd only said "waiguoren" and not "laowai." Beijingers are fairly invested in appearing modern and cosmopolitan and consider noticing foreigners at all to be uncouth peasant behavior.
That is definitely something I miss the hell out of about Beijing.