Are you a Vietnamese-American, or a naturalized American from Vietnam? If it's the former, stop calling yourself any hyphenated names or considering yourself that way, especially when dealing with Japanese. You are American. Period. If it's the latter, you are still American, but you will simply have to explain where you were born.
As for racism against Asians, what I just suggested will take care of a lot of it. Tell people you're American. The only real Asian racism going on here is against the Chinese or Koreans (largely). As for your other friends and family and their hates, I can only guess at why. Many have feelings against whole countries or nationalities, when they really only (unknowingly) just hate their governments or a select group that wronged them. Leave those feelings behind when you come here, of course.