Use the term "third world" with your clients and they may wish to no longer be your clients. It's pretty outdated and almost never used in a professional context any longer. http://www.npr.org/sections/goatsandsoda/2015/01/04/37268443...
I think this is a great illustration of the fact that, although some people intend to be derisive in their speech, we shouldn't assume that any designation whatsoever is intended as derision. That is, everybody needs to chill and assume the other person is making a good-faith attempt to be reasonably polite until proven otherwise.