The only people that ever told me "Don't say Frisco" where middle-aged white people from Los Altos/Mill Valley/Napa/et al. All the local kids, and there were many, that I went to school with at USF, 14 years ago, used the term "Frisco" regularly.
Not trying to hate on anybody. But this is simply not true in the real San Francisco today. And it hasn't been that way for a long time, actually.