I agree 'gweilo' and 'gweimui'' (white girl) are frequently used here by everyone (locals and foreign residents) who lives here in a very affectionate manner. There are other terms, ie 'fei lo' (fat guy), 'fei jai'(fat kid), 'go lo'(tall guy), etc that seem derogatory and condescending at face value too but are actually used as an affectionate greeting among friends and family. If you are addressed in such manner, take it as a sign that you are considered part of the group/community.
Reply to #6 clitty's post:
Though I am ethnically Chinese, I have been addressed as ''Gwai jai' too. In my context, it means that I still act and think like a Westerner though I look Chinese.
Actually I prefer being called 'gwai jai'' over ''juk sing jai' (overseas born Chinese) which I found to be more derogatory in meaning as it literally means 'bamboo character''. What is a bamboo? Bamboo is yellow on the outside but empty in the inside, implying that emptiness means 'no Chinese culture' or 'no culture at all''.