There were so many examples of racist costumes, mostly in the vein of "culture as a costume." If you don't know what I'm talking about, Google it. I'll wait. :)
And, while the cultural appropriation costumes go back a long time (such a long tradition of racism to celebrate, evidently), but there's an even more perverse issue when it becomes the Sexy Racist costume. At that point, we go beyond the problem of Sexy Halloween monopoly (meaning a woman cannot buy a pre-made costume that isn't uber sexified) and the devaluing of a huge, non-monolithic culture into one stereotype and we now sexualize that monolith, that stereotype. And that has huge consequences.
I hope that made sense. I didn't want this to be a long post. I highly encourage you to do tons of research on the subject because there's SO much more to be said than I can articulate.
Thankfully, I've spotted no Blackface pins, probably because at least costume manufacturers, while content to make money off of cultural appropriation and racism, seem to have some line they won't cross. That doesn't stop white people from taking it upon themselves to paint their faces to mimic another race every single damn year. Hey, people, stop it! Just stop it. No more blackface fullstop.