Can you dance? If you can't, how do you get out of it? Or do you do what I do?
Whenever this arises at parties I have a way of getting out of it and a good way of convincing someone you're a good dancer is to get them drunk. That way they won't be able to tell that you're actually horrible until their sober; at which point you make up reasons why you can't dance. Like, "Oh my heel hurts" or "I have Lupus so I can't dance". If they question you say, "Well I'm black so obviously I know how to dance silly" or just pimp slap them. Works like a charm.