Why is not knowing your heritage's language such a disgrace?

This is kind of a rant….Working at my parents’, I can’t tell you how many times daily I encounter people who constantly ask me if I know how to speak my “native” language from immigrants (African, Asian, etc). My native language is English since I was BORN here but I know they’re talking about my parents’ language.

The main reason I think I don’t know how to really speak Thai or Filipino fluently is because my parents are from different countries and they speak English to each other. 2 of the 5 siblings are fluent only because one loved Thai movies and the other one lived in Thailand for a short period of time.

Anyways, this man starts ranting at me in Tagolog (Filipino dialect) and then I said, “I’m sorry, I don’t understand.” he turns to his wife and says, “See? She doesn’t understand.” and shook his head and said I’m not a real Filipino and continued to “lecture” me in Tagolog until he made me feel bad and my eyes started to kind of tear up. It’s stupid but I’m pretty sensitive. Then he said he was just joking but still lectured me in a nicer way… but was saying it wasn’t right.

I don’t think it’s my fault. _