asking about ancestry is a good way. I’ve been asked during the first conversation and it hasn’t bothered me. It helped that it was a deep conversation and the topic was somewhat relevant. It makes all the difference if someone is trying to get to know you. I understand I look ethnically ambiguous and if I were trying to get to know me I’d be curious too.
I think I know how your dad feels. Growing up in West Coast US I didn’t understand why central Americans had such animosity towards being compared or mistaken as Mexican. Then I moved to the south. To my co workers every brown person was Mexican. “hey go ask your little amigo xy or z” was common. “what little amigo?” " The Mexican who’s got the keys to the gate" “I don’t know that guy. Also, he’s Guatemalan. See that flag hanging from his car? It’s a Guatemalan flag” I didn’t piss me off, but it made me feel a way I haven’t felt before and it’s not positive. I now get triggered when people just assume I’m Mexican. It says a lot about them and it’s not good.