Well, I "dance" when sober, and I enjoy it! It's a socially acceptable way to be close to, and touch, attractive members of the appropriate sex. Furthermore, the physical arousal caused by vigorous exercise tends to promote sexual arousal as well. Not to mention that watching people writhe to suggestive music is also extremely popular.

Then again, from a certain point of view, almost every kind of sexual activity is extremely ridiculous. I mean, you put the what in the where? That's disgusting! Who would want to do something like that?