>>The takeaway from this case: everybody should learn Spanish :). Thank you for sharing.
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>Avoiding Spanish is difficult if you live in California.
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>As a child I'd learned the phrases "Yo no se habla español" (I do not speak Spanish) and "Yo no comprendo español" (I do not understand Spanish) -- but apparently my pronunciation was too good (i.e. I didn't sound "gringo" enough) -- so folks assumed I was joking when I said it and continued talking to me as if I did understand Spanish.

There so many dialects and regional pronunciations of Spanish that Mexicans may think you are from Argentina; Argentinians think you are from Costa Rica, and Spaniards think you are just an illiterate Spaniard :). I have been studying Spanish for many, many years and still feel frustrated when I watch movies from different countries.
I began learning French three years ago and I love the fact that, for the most part, in all countries where they speak French, it is the same in terms of pronunciation (except, maybe, French Canadians).