The biggest take away I have gotten from this podcast:
Saying/doing racially inscensitive and hurtful things out of ignorance doesn't make you a racist, it's when you continue to do them after you know its hurtful.
Obviously many white people think it's hurtful when it is assumed they can't dance. Why would it be ok to keep making fun of them for it? I see no way you can justify the idea that it is insensitive to assume black people are good dancers but it's totally cool to assume white people are bad dancers.
In the end, if someone is a bad dancer make fun of them for it (or step up your kindness game of course). What do you gain by bringing race into it? There is plenty to lose because non-white people saying racially charged things makes white people mostly react one of two ways. Non-racists feel weird and generally don't know how to act going forward and racists use it as an excuse to say some seriously fucked up stuff. I don't think either of those outcomes are positive.
As always, when it doubt just leave race out of it and everyone will be happier.