"Lil Wayne"
Please don't tell me that superficially dressing up as a public figure of another race is going to be condemned in the next episode. Mingo wore an (accurate) braided wig, cap, and "diamond teeth." That's how you dress up as any celebrity: you use their most defining or wacky or joked-about features so everyone knows who you are. No one was mocking black people or black features in general (which was the case in black-face). They were having some fun with a particular public figure. It's widely understood that public figures are fair game (even the law sees it that way) - and in this case they weren't even saying anything unkind about him. More like cheering for him... with a sense of humor.
I suppose it's too much to ask for, but I really hope this isn't one of those things where the white kids take in a sober, self-flagellating lesson about microaggressions and the history of black-face. I wish it hadn't come up at all, but if the show has to go this way, I hope there will at least be some mutual understanding where the white kids get why Iris reacted that way but Iris gets that just because you can pick up a whiff of something racial, it doesn't necessarily mean anyone has done anything wrong.