For me, it's social dancing, specifically West Coast Swing. Because while there is just social dancing, and some who only do it, there's a bit of a culture of competition, and it has its own governing body for determining where you place in competitions, and when it does sound like a cult when described.
"Your entire conception of the world and your place in it is part of an elaborate prank that spans the history of all hitherto existing societies."
Oh I didn't see the word hobby