First of all welcome Sonny!
I don't mind that kind of joking at all. I really think it's all in fun, and will gladly joke back.
I too, since I've lived in California, am constantly mistaken for Mexican. I can't tell you how many times, be it at the store, or at work, I'll be the person that a stranger comes up to and starts rattling off in Spanish, assuming that I am Mexican. I couldn't believe it when I first moved here, but as you know California has a very very large Mexican population, and I guess I fit the mold.
On my desk at work I have a name plaque; my last name has double "L's" in it, which in Italian you'd "pronounce" if you were to say the name. Many times, people not knowing, will "not" pronounce the L's (they wouldn't be pronounced in Spanish) as they look at it and then say my name. I will always have to correct them.
Although I am use to it by now, I still just don't see that I look Mexican, but understand that their is such a large number of Mexicans that their logic in assuming I am makes sense. I am not offended, but must admit, on the very few occasions someone sees my name and says, "Are you Italian", I proudly answer yes, since it seems at times I'm the only Italian in California. :p
TIS