I think the college frat bro and the kid dressing up as Idris Elba are a couple of good examples.
For the kid, it's hero worship and what's wrong with that? Isn't that sort of a positive thing, racially speaking? If it's not, then why are there black Barbie dolls? Shouldn't that be offensive?
The frat bro might be doing it to be offensive. If so, what is the punishment? Should there even be one? I have generally found that the best "punishment" for jackasses is to ignore them. That doesn't seem to be a popular approach, especially among SJWs, because they can't get the last word in that way.
Also, slight tangent, one of my favorite Three Stooges shorts is "A Plumbing We Will Go". One scene in this short takes place in a kitchen, where the black cook is perplexed by water coming out of the stove and other appliances. He engages in slapstick routines like falling down, making faces, etc. Exactly the kind of stuff that Curly did on a regular basis. The Three Stooges are out of favor these days because of their political incorrectness and are not supposed to be watched by little kids. One of the nutball articles I read once used the above scene as an example (as well as several others that involved black or Japanese people - nothing about making fun of krauts though, which they did all the time).
ETA because three people posted while I was typing. Yeah, what about this Shaun King character?