I guess we just gotta live with other people's stereotypes at times. And some people cannot operate well under pressure (the stall uncle) so they just say things without thinking to much about it.
Just yesterday I was waiting for a tabao. My son was napping at home and I went downstairs to tabao my dinner. I of course would like to get home asap in case my son wakes and gets a scare for not seeing me around.
I waited a full half hour for a packet of noodles. Can you believe it? I was so hopping mad because I sat there and observed how they were dealing with orders. The people who were eating in and ordering dishes like vege, soups and meats, all got their orders first even though they came later than me! So it was pretty apparent to me that they were accumulating orders like fun, fried rice and the sorts so that they can mass produce them.
I confronted the boss of the zi char stall (who was very flustered because there were a lot of angry, hungry, waiting-for-their-tabao customers) and asked her why am I waiting so long for my order. She said, "Oh the kitchen is busy." I told her, "Is that so? People who came later and are eating in are getting their orders first. Shouldn't it be on a first come first serve basis?" She said, "Tabao people can usually wait."
After she said that I was soooo mad. I told her, "I think you better take back your statement and think it through again before answering me again."
Anyway, my point is, everyone has their own perception of things (the boss of that stall assumed that people who are tabao-ing shouldn't be in a hurry) as well as stereotypes. Sorry that you are met with such rude stall owners but that's what they're used to, seeing Chinese people speaking Mandarin. I know it's frustrating for you; just as it was frustrating for me in Europe when everyone thought I must be Japanese.
I guess.. It's just part of life... Sad to say... *Big Hugz*