I'm Irish and I don't get offended by that dude in a leprechaun costume over there.
That's good. But a leprechaun isn't a real person, and there's not a contemporary community of Leprechauns who are undergoing active colonialism and actively fighting misrepresentations. I totally feel for all those leprechauns living in poverty while the US government continues to systematically marginalize them through ongoing policies that ignore their inherent sovereignty and Indigenous rights to the land. While the Irish may have had a history of oppression in the US, no one can argue that they are still marginalized or would be categorized as anything other than part of the majority culture.
If that's too wordy?
Dude, Leprechauns aren't real people.
I'm Pocahontas/Tiger Lily/an Indian from Peter Pan/a historic figure/other fictional character!
That's cool, but all of those were based off of the same hurtful stereotypes. Have you SEEN Peter Pan? "What makes the red man red?"? Really? Pocahontas might seem like a "good" stereotype–but she's still an oversexualized woman who talks to animals and trees and is only famous because she saves a white dude. If you were the "real" pocahontas you'd also be 9-12 years old.