My impression had always been that for most Americans, the default "Asian" ethnicity in the minds of dumbass Americans was Chinese. Maybe it's regional?

The problem with "Oriental", in the US anyway, is that most Americans think it's an exact synonym for "Asian". I used to work for an Israeli who often referred to the Middle East, especially the food, as "Oriental". This is correct usage: They're east of here (some people think they're west as well, but those daffy Round Earthers are best ignored). Still, some cretin (from Baltimore, not Crete) in tech support digested that for a while and concluded that souvlaki is Chinese (this is part of my "impression" as seen in paragraph 1). He clung like grim death to the idea and would not be dissuaded! He decided that the local Chinese restaurant "wasn't for real" because they wouldn't give him any souvlaki, but he got over it because for some bizarre reason the Greek place would. Heh heh.

All sniderei aside, if you use the word "Oriental" (or any other word with more than one syllable) correctly in the US, you'll just confuse people. Have a heart! We're confused enough already.