No Stupid Questions

Others have given you solid answers on why the chicken and watermelon thing was really stupid so I'll try to answer from the Irish perspective on the second part of your question:

You can serve me corned beef and cabbage on St. Patrick's day as long as you're not being a dick about it. I'd probably consider it a nice effort actually if I happened to be abroad on the day.

My dad used to love corned beef, cabbage and potatoes with parsley sauce. It's a grand meal but not my thing.

If you were a unionist who served it to me in a leprechaun outfit I'd be inclined to tell you where to go though.

Edit: I hope this answers your question. It's a good question and the answer is nuanced so if I can offer you more perspective let me know, I'd be happy to help.

Wait, What's this about corned beef? I am Irish (as in actually from Ireland) and I have no idea what that has to do with St Patrick's day?

I think it's not really a holiday for sharing culture. I don't know, feel free to correct me if I'm wrong. Adopting black traditions is a touchy topic in the US. Some encourage it, and others decry it as appropriation. Considering that its a holiday commemorating the end of owning black people, I can see how 'appropriating' a tradition on that day might be found distasteful.

That said I personally think the concept or cultural appropriation is nonsense. You do not own your culture. That is for everyone. What you own is your own experiences. Those are yours and no one else's.

I'm a white man from Ukraine migrated to America in 1989.

I love fried chicken, I live in the south of America the deep South and man oh man do we have good fried chicken!

Fried chicken is a universally loved dish and is only stereotyped by the most ignorant of people!

Not only should fried chicken be served for Juneteenth it should be served on every holiday as well!

Probably a lot of black families actually do have fried chicken, barbeque and cookouts are apparently a big part of the festivities traditionally.

If you find yourself becoming such good friends with a black person that they actually invite you to one of these cookouts, don't bring fried chicken, or watermelons, or most of the stereotypical "black" foods, they're considered black people food because the post civil war south fostered an environment of chronic black poverty on purpose that led to black families tending towards raising cheaper animals and growing cheaper crops for their own consumption.

So a white guy cracking watermelon or fried chicken jokes or bringing that kind of stuff to a black celebration comes across less as trying to share in the culture and more as rubbing salt in a, in many ways still open, wound.

As for what you should bring, bro just ask. Just making it known ya want to bring something for folks to enjoy will be good and appreciated, and if they decide they'd like to take you up on that, they'll either give you a recipe off their list of stuff they've decided they want or ask what you think you can handle making and take your word on that if anything you feel confident making sounds good. Who knows, maybe that year will go down as the year that corned beef ya mentioned becomes a staple of the annual cookout!