We could say this is the most racist thing we've ever seen, but maybe it's just made worse because Mickey is smiling throughout it. Mickey's Mellerdrammer follows Mickey and the gang as they put on a production of—gulp—Uncle Tom's Cabin. Sure, that already sounds like a recipe for racism. But then Mickey puts on blackface. Mickey the Mouse... wears... blackface.
Blackface in Mickey's Mellerdrammer (1933)