I guess I should just be more standoffish about this question and let people think I’m an asshole.

thats kind of my thought, here. you're someone from a place they've never been (nor maybe met anyone from), and you're not the living expectation of said place. that is incredibly interesting to people! and most people will be offended or sketched out if you simply ignore their question, or tell them that you don't want to answer it. from their point of view, its cool that you are (nationality) and they would likely be excited to identify as (nationality).

we will never be able to change others. we can only change how we react to them. you may as well focus on being yourself, not worrying about other people, and accepting that this is what most people will ask you first about.

personally, i would create some sort of go-to answer. im from the midwest so its really hard for me not to genuinely connect with other humans who want to speak with me. i would say "ah, yeah, my parents are from X, i was born here. i do/dont go back every so often. whats your heritage?".