Actually lots of people do have their friends filming them dancing alot of them do shuffle dancing that they practice and like to post videos of themselves doing it at festivals. I follow a few cos i loce that style....have you been to any yourself?
And if you are joining in on a social media trend then duh of course you might practice it first then film it or have someone film it for you and post it...that is the whole point of those viral trends, otherwise it wouldn't be trending.
Why does dancing have to be good though? Dance is about expressing yourself how you feel. Why is it embarrassing to dance with your partner and post a video of you doing it?